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SUN  SODIUM        HYDROGEN  STAR,  NEBUUE 

SPECTRUM  ALDEBARAN 


A    SHORT    HISTORY 


OF 


NATURAL    SCIENCE 


A.ND    OF    THE 


PROGRESS  OF  DISCOVERY  FROM  THE  TIME  OF  THE 
.    GREEKS   TO    THE    PRESENT   DAY 


FOR     THE     USE    OF    SCHOOLS    AND    YOUNG    PERSONS 

By  ARABELLA  :^"bUCKLEY      - 


WITH     ILLUSTRATIONS 

BOSTON  COVkJm^  UBI^AKY 
CHESTKUT  HII^  M^^^ 

^  NEW  YORK: 
D.    APPLETON    AND    COMPANY, 

549  AND  551  Broadway. 
1876. 


67073 


f  0  i^t  9^mox^  of 

MY    BELOVED    AND    REVERED    FRIENDS 

SIR  CHARLES  and   LADY  LYELL 

TO     WHOM     I     OWE     MORE     THAN     I     CAN     EVER    EXPRESS 

TRUSTING  THAT  IT  MAY    HELP 

TO     DEVELOPE     IN     THOSE    WHO     READ     IT    THAT 

EARNEST    AND    TRUTH-SEEKING     SPIRIT    IN    THE    STUDY    OF     GOD'S 

WORKS    AND     LAWS    WHICH    WAS    THE    GUIDING 

PRINCIPLE      OF     THEIR     LIVES 


i 


PREFACE 


It  is  not  without  some  anxiety  that  I  offer  this  Httle 
work  to  the  public,  for  it  is,  I  believe,  the  first  at- 
tempt which  has  been  made  to  treat  the  difficult 
subject  of  the  History  of  Science  in  a  short  and 
simple  way.i 

Its  object  is  to  place  before  young  and  unscien- 
tific people  those  main  discoveries  of  science  which 
ought  to  be  known  by  every  educated  person,  and  at 
the  same  time  to  impart  a  living  interest  to  the  whole, 
by  associating  with  each  step  in  advance  some  history 
of  the  men  who  made  it. 

During  the  many  years  that  I  enjoyed  the  privi- 
lege of  acting  as  secretary  to  the  late  Sir  Charles 
Lyell,  and  was  thus  brought  in  contact  with  many  of 
the  leading  scientific  men  of  our  day,  I  often  felt  very 
forcibly  how  many  important  facts  and  generaliza- 
tions of  science,  which  are  of  great  value  both  in  the 
formation  of  character  and  in  giving  a  true  estimate 

*  Mr.  Baden  Powell's  excellent  little  '  History  of  Natural  Philo- 
sophy,' published  in  Lardner's  'Cyclopaedia'  in  1834,  is  scarcely 
intended  for  beginners,  and  does  not  extend  farther  than  the  seven- 
teenth century.  This  is  the  only  work  of  the  kind  I  have  been  able  to 
find. 


VL  PREFACE, 


of  life  and  its  conditions,  are  totally  unknown  to  the 
majority  of  otherwise  well-educated  persons. 

Great  efforts  are  now  being  made  to  meet  this 
difficulty,  by  teaching  children  a  few  elementary  facts 
of  the  various  branches  of  science  ;  but,  though  such 
instruction  is  of  immense  value,  something  more  is 
required  in  order  that  the  mind  may  be  prepared  to 
follow  intelligently  the  great  movement  of  modern 
thought.  The  leading  principles  of  science  ought 
in  some  measure  to  be  understood ;  and  these  will, 
I  believe,  be  most  easily  and  effectually  taught  by 
showing  the  steps  by  which  each  science  has  attained 
its  present  importance. 

It  is  this  task  which  I  have  endeavoured  to  ac- 
complish ;  and  if  teachers  will  make  their  pupils  master 
the  explanations  given  in  these  pages  and,  wherever 
it  is  possible,  try  the  experiments  suggested,  I  venture 
to  hope  that  this  little  work  may  supply  that  modest 
amount  of  scientific  information  which  everyone 
ought  to  possess,  while,  at  the  same  time,  it  will  form 
a  useful  groundwork  for  those  who  wish  afterwards  to 
study  any  special  branch  of  science. 

The  plan  adopted  has  been  to  speak  of  discoveries 
in  their  historical  order,  and  to  endeavour  to  give  such 
a  description  of  each  as  can  be  understood  by  any 
person  of  ordinary  intelligence.  This  has  made  it 
necessary  to  select  among  subjects  of  equal  impor- 
tance those  which  could  be  dealt  with  in  plain  lan- 
guage, and  to  avoid  passing  allusions  to  such  as  did 
not  admit  of  such  explanation. 


PREFACE.  vii 


The  history  of  the  nineteenth  century  has  been  a 
very  difficult  and  I  fear  scarcely  a  successful  task ; 
for,  while  those  who  know  anything  of  the  subjects 
mentioned,  will  feel  that  the  accQunt  is  very  defective 
owing  to  so  much  being  left  out,  the  beginner  will 
probably  find  it  difficult  owing  to  so  much  being  put 
in.  The  reproach  on  both  sides  would  be  just,  yet  it 
seemed  better  to  give  even  a  few  of  the  leading  dis- 
coveries and  theories  of  our  own  time  than  to  leave 
the  student  with  such  crude  ideas  of  many  branches 
of  science  as  he  must  have  had  if  the  history  had 
ended  with  the  eighteenth  century. 

When  treating  of  such  varied  subjects,  many  of 
them  presenting  great  difficulties  both  as  regards 
historical  and  scientific  accuracy,  I  cannot  expect  to 
have  succeeded  equally  in  all,  and  must  trust  to  the 
hope  of  a  future  edition  to  correct  such  grave  errors 
as  will  doubtless  be  pointed  out,  in  spite  of  the  care 
with  which  I  have  endeavoured  to  verify  the  state- 
ments made. 

As  the  size  of  the  book  makes  it  impossible  to 
give  the  numerous  references  which  would  occur  on 
every  page,  I  have  named  at  the  end  of  each  chapter 
a  few  of  the  works  consulted  in  its  preparation,  choos- 
ing always  in  preference  those  which  will  be  useful  to 
the  reader  if  he  cares  to  refer  to  them.  I  had  also 
prepared  questions  on  the  work  ;  but  those  competent 
to  give  an  opinion,  tell  me  that  teachers  in  these  days 
prefer  to  prepare  their  own  lessons.  I  have  there- 
fore substituted,  at  p.  439,  a  chronological  table  of  the 


viii  PREFACE. 

various  sciences,  by  means  of  which  questions  can  be 
framed,  either  upon  the  discoveries  of  any- given 
period,  or  on  the  progressive  advance,  through  several 
centuries,  of  any  of  the  five  main  divisions  of  science 
which  are  dealt  with  in  this  volume. 

In  conclusion,  I  wish  to  acknowledge  my  obliga- 
tions to  many  kind  friends,  and  especially  to  Mr.  A. 
R.  Wallace  and  Mr.  J.  C.  Moore,  F.R.S.,  who  have 
rendered  me  very  material  and  valuable  assistance. 
I  am  also  much  indebted  to  the  Rev.  R.  M.  Luckock,  of 
the  Godolphin  Grammar  School,  who  read  the  whole 
work  in  manuscript,  with  a  view  to  pointing  out  any 
portions  which  might  be  unintelligible  to  schoolboys. 

London  :  December  1875. 


CONTENTS. 


PAGE 

Introduction ,        ,        .      i 


PART    I. 

SCIENCE   OF  THE  GREEKS. 

CHAPTER    I. 

639  TO  470  B.C. 

Ignorance  of  the  Greeks  concerning  Nature — Ionian  School  of 
Learning — Thales  discovers  the  Solstices  and  Equinoxes,  and 
knows  that  the  Moon  Reflects  the  Light  of  the  Sun — Anaxi- 
mander  invents  a  Sun-dial — Discovers  the  Phases  of  the  Moon — 
Makes  a  Map  of  the  Ancient  World — Pythagoras  teaches  that 

■  the  Earth  moves,  and  that  the  Morning  and  Evening  Star  are 
the  same — He  studies  Geology,  and  knows  that  Land  has  in 
some  places  become  Sea — True  sayings  of  Pythagoras  and  his 
Followers  about  Geology  .......       7 

CHAPTER    n. 

499  TO  322  B.C. 

Anaxagoras  studies  the  Moon — Describes  Eclipses  of  the  Sun  and 
Moon — Is  Tried  and  Condemned  for  Denying  that  the  Sun  is  a 
God — Hippocrates  the  Father  of  Medicine — Separates  the 
office  of  Priest  and  Doctor —  Studies  the  Human  Body  — 
Eudoxus  has  an  Observatory — Makes  a  Map  of  the  Stars — 
Explains  the  Movements  of  the  Planets — Democritus  studies 
the  Milky  Way — Aristotle  an  Astronomer  and  Zoologist — 
Divides  Animals  into  Classes — Teaches  that  there  is  a  Gradual 
Succession  of  Animal  Life — Studies  the  Difference  of  the  Life  in 
Plants  and  Animals — Theophrastus  the  first  Botanist  .         -13 


CONTENTS. 


CHAPTER    III. 
320  TO  212  B.C. 

PAGE 

School  of  Science  at  Alexandria — The  Ecliptic  and  the  Zodiac — 
Greeks  believed  that  the  Sun  moved  round  the  Earth — Aristar- 
chus  knew  that  it  was  the  Earth  which  moved — He  also  knew 
of  the  Obliquity  of  the  Ecliptic,  and  that  the  Seasons  are  caused 
by  it — He  knew  that  the  Earth  turns  daily  on  its  Axis — Euclid 
discovers  that  Light  travels  in  straight  lines— Archimedes  dis- 
covers the  Lever — Principle  of  the  Lever — Hiero's  Crown,  and 
how  Archimedes  discovered  the  principle  of  Specific  Gravity — 
Screw  of  Archimedes       .         .         .         .         .         .         .         .18 


CHAPTER     IV. 

280  TO  120  B.C. 

Erasistratus  and  Herophilus  study  the  Human  Body — Eratosthenes 
the  Geographer  lays  down  the  First  Parallel  of  Latitude  and  the 
First  Meridian  of  Longitude — He  measures  the  Circumference  of- 
the  Earth — Hipparchus  writes  on  Astronomy — Catalogues  1,080 
Stars — Calculates  when  Eclipses  will  take  place — Discovers  the 
Precession  of  the  Equinoxes     .  .         .         .         .         .         .25 

CHAPTER  V. 

FROM  A.D.   70  TO  200. 

Ptolemy  founds  the  Ptolemaic  System — He  writes  on  Geography 
— Strabo,  a  great  traveller,  writes  on  Geography  —  Studies 
Earthquakes  and  Volcanoes — Galen  the  greatest  Physician  of 
Antiquity —  Describes  the  Two  Sets  of  Nerves — Proves  that 
Arteries  contain  Blood — Lays  down  a  theory  of  Medicine — 
Greece  and  her  Colonies  conquered  by  Rome — Decay  of  Science 
in  Greece — Concluding  remarks  on  Greek  Science  .         .         32 


CONTENTS.  xi 


PART    II. 

SCIENCE   OF  THE  MIDDLE  AGES, 

CHAPTER  VL 

SCIENCE  OF  THE  ARABS. 

PAGE 

Dark  Ages  of  Europe — Taking  of  Alexandria  by  the  Arabs,  and 
burning  of  the  Library — The  Arabs,  checked  in  their  conquests 
by  Charles  Martel,  settle  down  to  Science — The  Nestorians 
and  Jews  translate  Greek  Works  on  Science — Universities  of  the 
Arabs — Chemistry  first  studied  by  the  Arabs — Alchemy,  or  the 
attempt  to  make  Gold — Hermes  the  first  Alchemist — Hermeti- 
cally-sealed Tubes — Gases  and  Vapours  called  '  Spirits '  by  the 
Arabs — The  use  of  this  Word  retained  by  us     .         .         .         .39 

CHAPTER   VII. 
SCIENCE  OF  THE  ARABS   (CONTINUED). 

Geber,  or  Djafer,  the  founder  of  Chemistry — His  Explanation  of 
Distillation — Of  Sublimation — Discovers  that  some  Metals  in- 
crease in  weight  when  heated — Discovers  strong  Acids — Nitric 
Acid — Sulphuric  Acid — Discovery  of  Sal-Ammoniac  by  the 
Arabs — Arabs  mix  up  Astronomy  with  Astrology — Albateg- 
nuis  calculates  the  Length  of  the  Year — Mohammed  Ben  Muse, 
first  writer  on  Algebra — Uses  the  Indian  Numerals — Gerbert 
introduces  them  into  Europe — Alhazen's  discoveries  in  Optics — 
His  Explanation  why  only  one  image  of  each  object  reaches  the 
Brain — His  discovery  of  Refraction,  and  of  its  effect  on  the  light 
of  the  Sun,  Moon,  and  Stars — His  discovery  of  the  magnifying 
power  of  rounded  glas^ses  .......     43 

CHAPTER  VIII. 

SCIENCE  OF  THE  MIDDLE  AGES  IN  EUROPE.      ' 

Roger  Bacon — His  *  Opus  Majus ' — His  Explanation  of  the  Rain- 
bow—He makes  Gunpowder — Studies  Gases — Proves  a  Candle 
will  not  burn  without  Air — His  Description  of  a  Telescope — 
Speaks  of  Ships  going  without  Sails — Flavio  Gioja  invents  the 


xii  CONTENTS. 


Mariner's  Compass — Greeks  knew  of  the  Power  of  the  Load- 
stone to  attract  Iron — Use  of  the  Compass  in  discovering  new 
lands — Invention  of  Printing — Columbus  discovers  America — 
Vasco  de  Gama  sees  the  Stars  of  the  Southern  Hemisphere — 
Magellan's  ship  sails  round  the  World — Inventions  of  Leonardo 
da  Vinci.  .         .         .  .         .  .  .  .         .  •     5  ^ 


PART    III. 

RISE  AND  PROGRESS  OF  MODERN  SCIENCE. 

CHAPTER   IX. 

SCIENCE  OF  THE  SIXTEENTH  CENTURY. 

Rise  of  Modem  Science — Dogmatism  of  the  Middle  Ages — 
Reasons  for  studying  Discoveries  in  the  order  of  their  dates — 
Copernican  theory  of  the  Universe — Copernicus  goes  back  to 
the  System  of  Aristarchus — Is  afraid  to  publish  his  Work  till 
quite  the  end  of  his  Life — Work  of  Vesalius  on  Anatomy — He 
shows  that  Galen  made  many  mistakes  in  describing  Man's 
Structure — His  Banishment  and  Death — The  value  of  his  Work 
to  Science— Fallopius  and  Eustachius  Anatomists — Gesner's 
Works  on  Animals  and  Plants — He  forms  a  Zoological  Cabinet 
and  makes  a  Botanical  Garden — His  Natural  History  of  Animals 
— His  classification  of  Plants  according  to  their  Seeds — His 
work  on  Mineralogy — Csesalpinus  makes  the  First  System  of 
Plants  on  Gesner's  plan — Explains  Dioecious  Plants — Chemistry 
of  Paracelsus  and  Van  Helmont       ...... 

CHAPTER  X. 

SCIENCE  OF  THE   SIXTEENTH   CENTURY   (CONTINUED). 

Baptiste  Porta  discovers  the  Camera  Obscura — Shows  that  our 
Eye  is  like  a  Camera  Obscura — Makes  a  kind  of  Magic  Lantern 
by  Sunlight — Kircher  afterwards  makes  a  Magic  Lantern  by 
Lamplight — Dr.  Gilbert's  discoveries  in  Electricity — Tycho 
Brahe,  the  Danish  Astronomer — Builds  an  Observatory  on  the 
Island  of  Huen — Makes  a  great  number  of  Observations,  and 


CONTENTS.  xiii 


PAGE 

draws  up  the  Rudolphine  Tables  —Galileo  discovers  the  principle 
of  the  Pendulum — Calculates  the  velocity  of  Falling  Bodies,  and 
shows  why  it  increases — Shows  that  Unequal  Weights  fall  to  the 
Ground  in  the  same  time — Establishes  the  relations  of  Force  and 
Weight — Stevinus  on  Statics  —Summary  of  the  Science  of  the 
sixteenth  century 74 


CHAPTER   XI. 
SCIENCE   OF  THE   SEVENTEENTH   CENTURY. 

Astronomical  discoveries  of  Galileo — The  Telescope — Galileo  ex- 
amines the  Moon,  and  discovers  the  Earth-light  upon  it — Dis- 
covers Jupiter's  four  Moons — Distinguishes  the  Fixed  Stars  from 
the  Planets — The  phases  of 'Venus  confirm  the  Copernican  theory 
— Galileo  notices  Saturn's  Ring,  but  does  not  distinguish  it 
clearly — Observes  the  spots  on  the  Sun — The  Inquisition  force 
him  to  deny  the  movement  of  the  Earth —  Blindness  and  Death 
of  Galileo       ..........     87 

CHAPTER  Xn. 
SCIENCE  OF  THE   SEVENTEENTH   CENTURY   (CONTINUED). 

Kepler  the  German  Astronomer — Succeeds  Tycho  as  Mathema- 
tician to  the  Emperor  Rudolph — His  description  of  the  Eye — 
He  tries  to  explain  the  orbit  of  the  planet  Mars — And  by  com- 
paring Tycho's  tables  with  observation  discovers  his  First  and 
Second  Law  of  the  movements  of  the  Planets — His  delight  at 
Galileo's  discoveries — Kepler's  Third  Law — Comparison  of  the 
labours  of  Tycho,  Galileo,  and  Kepler      .         .         .         .         -95 

CHAPTER  XIIL 

SCIENCE  OF  THE  SEVENTEENTH  CENTURY   (CONTINUED). 

Francis    Bacon,    1561-1626 — He    teaches    the    true    method    of 
■    studying  Science  in  his  'Novum  Organum' — Rene  Descartes, 
1 596-1 650 — He  teaches  that  Doubt  is  more  honest  than  Ignorant 
Assertion — Willebrord   Snellius   discovers  the  Law  of  Refrac- 
tion, 1621 — Explanation  of  this  Law         .....    103 


xiv  CONTENTS. 


CHAPTER   XIV. 
SCIENCE  OF  THE  SEVENTEENTH   CENTURY   (CONTINUED). 

PAGE 

Fabricius  Aquapendente  discovers  Valves  in  the  Veins^Harvey's 
discovery  of  the  Circulation  of  the  Blood — Discovery  of  the 
Vessels  which  carry  nourishment  to  the  Blood — Gaspard  Asellius 
notices  the  Lacteals — Pecquet  discovers  the  Passage  of  the  fluid 
to  the  Heart — Riidbeck  discovers  the  Lymphatics     .         .         .no 

CHAPTER   XV. 
SCIENCE  OF  THE    SEVENTEENTH    CENTURY   (CONTINUED). 

Torricelli  discovers  the  reason  of  Water  rising  in  a  Pump — Uses 
Mercury  to  measure  the  Weight  of  the  Atmosphere — Makes  the 
First  Barometer — M.  Perrier,  at  Pascal's  suggestion,  demon- 
strates variations  in  the  pressure  of  the  atmosphere — Otto 
Guericke  invents  the  Air-pump — Working  of  the  Air-pump — 
Guericke  proves  the  Pressure  of  the  Atmosphere  by  the  experi- 
ment of  the  Magdeburg  Spheres — He  makes  the  first  Electrical 
Machine — Foundation  of  Royal  Society  of  London  and  other 
Academies  of  Science      .         .         .         .         .         .         .         .116 

CHAPTER   XVI. 
SCIENCE   OF   THE  SEVENTEENTH   CENTURY   (CONTINUED). 

Boyle's  Law  of  the  Compressibility  of  Gases — ^This  same  Law  dis- 
covered independently  by  Marriotte — Hooke's  theory  of  Air 
being  the  cause  of  Fire — Boyle's  experiments  with  Animals 
under  the  Air-pump — ^John  Mayow,  the  greatest  Chemist  of  the 
Seventeenth  Century — His  experiments  upon  the  Air  used  in 
Combustion — Proves  that  the  same  portion  is  used  in  Respira- 
tion— Proves  that  Air  which  has  lost  its  Fire-air  is  Lighter — 
MayoVs  '  Fire-air '  was  Oxygen,  and  his  Lighter  Air  Nitrogen 
— He  traces  out  the  effect  which  Fire-air  produces  in  Animals 
when  Breathing      .         .         .         .         .         .         .         .         .128 


CONTENTS. 


CHAPTER  XVII. 
SCIENCE  OF  THE   SEVENTEENTH   CENTURY   (CONTINUED). 

PAGE 

Malpighi  first  uses  the  Microscope  to  examine  Living  Stmctures 
— He  describes  the  Air-cells  of  the  Lungs — Watches  the  Circula- 
tion of  the  Blood  —Observes  the  Malpighian  Layer  in  the  Human 
Skin — Describes  the  structure  of  the  Silkworm — Leeuwenhoeck 
discovers  Animalcules — Grew  and  Malpighi  discover  the  Cellular 
Structure  of  Plants — The  Stomates  in  Leaves — They  study  the 
Germination  of  Seeds — Ray  and  Willughby  classify  and  describe 
Animals  and  Plants — The  Friendship  of  these  two  Men     .         •    137 

CHAPTER   XVIII. 

SCIENCE   OF   THE   SEVENTEENTH  CENTURY   (CONTINUED). 

1642,  Birth  of  Newton — His  Education — 1666,  His  three  great 
Discoveries  first  occur  to  him — Method  of  Fluxions  and  Dif- 
ferential Calculus — First  Thought  of  the  Theory  of  Gravitation 
— Failure  of  his  Results  in  consequence  of  the  Faulty  Measure- 
ment of  the  size  of  the  Earth — 1682,  Hears  of  Picart's  new 
Measurement — Works  out  the  result  correctly,  and  proves  the 
Theory  of  Gravitation — Explanation  of  this  Theory — Establishes 
the  Law  that  Attraction  varies  inversely  as  the  squares  of  the 
distance — 1687,  Publishes  the  'Principia' — Some  of  the  Pro- 
blems dealt  with  in  this  Work .         .         .         .         .         .         .147 

CHAPTER  XIX. 

SCIENCE  OF  THE  SEVENTEENTH  CENTURY   (CONTINUED) 

Transits  of  Mercury  and  Venus — Kepler  foretells  their  occurrence 
— 163 1,  Gassendi  observes  a  Transit  of  Mercury — 1639,  Hor- 
rocks  foretells  and  observes  a  Transit  of  Venus — 1676,  Halley 
sees  a  Transit  of  Mercury,  and  it  suggests  to  him  a  method  for 
Measuring  the  Distance  of  the  Sun — 1691-1716,  Halley  de- 
scribes this  method  to  the  Royal  Society — Explanation  of 
Halley's  method 156 


CONTENTS. 


CHAPTER  XX. 
SCIENCE  OF  THE  SEVENTEENTH  CENTURY  (CONTINUED). 

PAGE 

Newton's  Discovery  of  the  Dispersion  of  Light — Traces  the 
amount  of  Refraction  of  each  of  the  Coloured  Rays — Makes  a 
Rotating  Disc  turning  the  colours  of  the  Spectrum  into  White 
Light — Reason  why  all  Light  passing  through  glass  is  not 
Coloured — Mr.  Chester  More  Hall  discovers  the  Difference  of 
Dispersive  Power  in  Flint  and  Crown  Glass — Newton's  Papers 
destroyed  bvhis  pet  dog — Last  years  of  Newton's  life         .         .164 

CHAPTER  XXL 

SCIENCE  OF  THE   SEVENTEENTH   CENTURY   (CONTINUED). 

Roemer  measures  the  Velocity  of  Light — Newton's  Corpuscular 
Theory  of  Light — Undulatory  or  Wave  Theory  proposed  by 
Huyghens — Invention  of  Cycloidal  Pendulums  by  Huyghens — 
Discovery  of  Saturn's  Ring — Sound  caused  by  Vibration  of  Air — 
Light  by  Vibration  of  Ether — Reasons  why  we  see  Light — 
Reflection  of  Waves  of  Light — Cause  of  Colour — Refraction 
explained  by  the  Undulatory  Theory — Mr.  Tylor's  Illustration 
of  Refraction — Double  Refraction  explained  by  Huyghens — 
Polarisation  of  Light  not  understood  till  the  nineteenth  century    .    1 72 

CHAPTER  XXIL 

Summary  of  the  Science  of  the  Seventeenth  Century    .  182 


CHAPTER    XXin. 

SCIENCE   OF   THE   EIGHTEENTH   CENTURY. 

Great  spread  of  Science  in  the  Eighteenth  Century — Advance  of 
the  Sciences  relating  to  Living  Beings — Foundation  of  Leyden 
University  in  1574 — Boerhaave,  Professor  of  Medicine  at  Ley- 
den, 1 701 — Foundation  of  Organic  Chemistry  by  Boerhaave — 
Influence  of  Boerhaave  upon  the  study  of  Medicine — Belief  of 
the  Alchemists  in  '  Vital  Fluids ' — Boerhaave's  Experiments  on 
the  Juices  of  Plants — Dr.  Hales's  Experiments  on  Plants — Boer- 
haave's Analyses  of  Milk,  Blood,  &c. — Great  popularity  of  his 
Chemical  Lectures  ,         .         .  .         .         .         .         .         .189 


CONTENTS. 


CHAPTER   XXIV. 

SCIENCE  OF  THE  EIGHTEENTH  CENTURY   (CONTINUED). 

PAGE 

Childhood  of  Haller — Foundation  of  the  University  of  Gottingen 
in  1736 — Haller  made  Professor  of  Anatomy — Haller's  Ana-  ■ 
tomical  Plates — He  discovers  the  power  of  Contraction  of  the 
Muscles — Rise  of  Comparative  Anatomy — John  Hunter's  in- 
dustry in  Dissecting  and  Comparing  the  Structures  of  different 
Animals — His  Museum  and  the  arrangement  of  his  Collection — 
Bonnet's  Experiments  on  Plants — Experiments  upon  Animals  by 
Bonnet  and  Spallanzani — Regrowth  of  different  parts  when  cut 
off — Bonnet's  theory  of  Gradual  Development  of  Plants  and 
Animals — Anatomical  Works  of  Haller — He  discovers  the 
power  of  the  Muscles  to  contract      .         .         .         .         .         -195 

CHAPTER    XXV. 

SCIENCE  OF  THE   EIGHTEENTH  CENTURY  (CONTINUED). 

Birth  and  Early  Life  of  Bufifon  and  Linnaeus  compared — Bufifon's 
Work  on  Natural  History — Daubenton  wrote  the  Anatomical 
Part — Buffon's  Books  very  interesting,  but  not  always  accurate — 
He  first  worked  out  the  Distribution  of  Animals — Struggles  of 
Linnaeus  with  Poverty — Mr.  Clifford  befriends  him — He  becomes 
Professor  at  Upsala — He  was  the  first  to  give  Specific  Names  to 
Animals  and  Plants — Explanation  of  his  Descriptions  of  Plants 
— Use  of  the  Linnaean  or  Artificial  System — Afterwards  super- 
seded by  the  Natural  System — Linnaeus  first  used  accurate  terms 
in  describing  Plants  and  Animals — Character  of  Linnaeus — Sale 
of  his  Collection,  and  Chase  by  the  Swedish  Man-of-war  .         .  204 


CHAPTER    XXVL 

SCIENCE  OF  THE  EIGHTEENTH  CENTURY  (CONTINUED). 

The  Study  of  the  Earth  neglected  during  the  Dark  Ages — Preju- 
dices concerning  the  Creation  of  the  World — Attempts  to  Ac- 
count for  Buried  Fossils — Palissy,  the  Potter,  first  asserted  that 
Fossil-shells  were  real  Shells — Scilla's  Work  on  the  Shells  of 
Calabria,  1670 — Woodward's  Description  of  Different  Fonna- 
tions,  1695 — Lazzaro  Moro  one  of  the  first  to  give  a  true  expla- 


-^^iii  CONTENTS. 


PAGE 

nation  of  the  facts — Abraham  Werner  lectures  on  Mineralogy 
and  Geology,  I775 — Disputes  between  the  Neptunists  and  Vul- 
canists — Dr.  Hutton  first  teaches  that  it  is  by  the  Study  of  the 
Present  that  we  can  understand  the  Past — Theory  of  Hutton — 
Sir  J.  Hall's  Experiments  upon  Melted  Rocks — Hutton  dis- 
covers Granite  Veins  in  Glen  Tilt — William  Smith,  the  *  Father 
of  English  Geologists ' — His  Geological  Map  of  England  .         .   214 


CHAPTER    XXVII. 

SCIENCE  OF  THE  EIGHTEENTH  CENTURY   (CONTINUED). 

Birth  of  Modem  Chemistry — Discovery  of  'Fixed  Air,'  or  Car- 
bonic Acid,  by  Black  and  Bergmann — Working  out  of  '  Che- 
mical Affinity '  by  Bergmann — He  tests  Mineral  Waters,  and 
proves  '  Fixed  Air '  to  be  an  Acid — Discovery  of  Hydrogen  by 
Cavendish — He  investigates  the  Composition  of  Water — Oxygen 
discovered  by  Priestley  and  Scheele — Priestley's  Experiments — 
He  fails  to  see  the  true  bearing  of  his  Discovery — His  Political 
Troubles  and  Death — Nitrogen  described  by  Dr.  Rutherford — 
Lavoisier  lays  the  Foundation  of  Modern  Chemistry — He 
destroys  the  Theory  of  '  Phlogiston  '  by  proving  that  Combustion 
and  Respiration  take  up  a  Gas  out  of  the  Air — Discovers  the 
Composition  of  Carbonic  Acid  and  the  nature  of  the  Diamond — 
French  School  of  Chemistry — Death  of  Lavoisier      .         .         .  225 

CHAPTER   XXVIII. 

SCIENCE  OF  THE   EIGHTEENTH  CENTURY   (CONTINUED). 

Doctrine  of  Latent  Heat,  taught  by  Dr.  Black  in  1760 — Water 
containing  Ice  remains  always  at  0°  C,  and  Boiling  Water  at 
100°  C,  however  much  Heat  is  added — Black  showed  that  the 
lost  Heat  is  absorbed  in  altering  the  condition  of  the  Water — 
Watt's  Application  of  the  Theory  of  Latent  Heat  to  the  Steam- 
engine — Early  History  of  Steam-engines — Newcomen's  Engine 
— Watt  invents  the  Separate  Condenser — Diagram  of  Watt's 
Engine — Difficulties  of  Watt  and  Boulton  in  introducing  Steam- 
engines  ...........   241 


CONTENTS.  xLc 


CHAPTER    XXIX.. 

SCIENCE  OF  THE   EIGHTEENTH  CENTURY  (CONTINUED). 

PAGE 

Benjamin  Franklin,  born  1706 — His  Early  Life — Du  Faye  dis- 
covers two  kinds  of  Electricity — Franklin  proves  that  Electricity 
exists  in  all  Bodies,  and  is  only  developed  by  Friction — Positive 
and  Negative  Electricity — Franklin  draws  down  Electricity  from 
the  Sky — Invents  Lightning-conductors — Discovery  of  Animal 
Electricity  by  Galvani — Controversy  between  Galvani  and  Volta 
— Volta  proves  that  Electricity  can  be  produced  by  the  Contact 
of  two  Metals — Electrical  Batteries — The  Crown  of  Cups — The 
Voltaic  Pile    ..........  253 


CHAPTER    XXX. 

SCIENCE  OF   THE  EIGHTEENTH  CENTURY  (CONTINUED). 

Bradley  and  Delisle,  Astronomers — Aberration  of  the  Fixed  Stains 
— Nutation  of  the  Axis  of  the  Earth,  Delisle's  Method  of  Mea- 
suring the  Transit  of  Venus — Lagrange  and  Laplace — Libration 
of  the  Moon  accounted  for  by  Lagrange — Laplace  works  out  the 
Long  Inequality  of  Jupiter  and  Saturn — Lagrange  proves  the 
Stabihty  of  the  Orbits  of  the  Planets — Sir  William  Herschel 
constructs  his  own  Telescopes — Discovery  of  a  New  Planet — • 
Discovery  of  Binary  Stars — Herschel  studies  Star-clusters  and 
Nebulae — Theory  of  Nebulae  being  matter  out  of  which  Stars 
are  made — The  Motion  of  our  Solar  System  through  Space — 
Weight  of  the  Earth  determined  by  the  Schehallien  Experiment 
— Summary  of  the  Science  of  the  Eighteenth  Century       .         .  265 


CHAPTER   XXXI. 

SCIENCE  OF  THE  NINETEENTH  CENTURY. 

Difficulties  of  Contemporary  History— ^.Discovery  of  Asteroids  and 
Minor  Planets  between  Mars  and  Jupiter — Dr.  Gibers  suggests 
they  may  be  fragments  of  a  larger  Planet — Encke's  Comet,  and 
the  correction  of  the  size  of  Jupiter  and  Mercury — Biela's 
Comet,  noticed  in  1826 — It  divides  into  two  Comets  in  1845 — 


CONTENTS. 


PAGE 

Irregular  movements  of  Uranus — Adams  and  Leverrier  calculate 
the  position  of  an  Unknown  Planet — Neptune  found  by  these 
calculations  in  1846  —A  Survey  of  the  whole  Heavens  made  by 
Sir  John  Herschel — His  work  in  Astronomy — Comets  and 
Meteor-systems        .........  287 


CHAPTER   XXXII. 

SCIENCE  OF  THE  NINETEENTH  CENTURY  (CONTINUED). 

Discoveries  concerning  Light  made  in  the  Nineteenth  Century — 
Birth  and  History  of  Dr.  Young — He  explains  the  Interference 
of  Light — Cause  of  Prismatic  Colours  in  a  Shadow — And  in  a 
Soap-bubble — Malus  discovers  the  Polarisation  of  Light  caused 
by  Reflection — Birth  and  History  of  Fresnel — Polarisation  of 
Light  explained  by  Young  and  Fresnel — Complex  Vibrations  of 
a  Ray  of  Light — How  these  Waves  are  reduced  to  two  separate 
Planes  in  passing  through  Iceland-spar — Sir  Da,vid  Brewster 
and  M.  Biot  explain. the  colours  produced  by  Polarisation  .         .   302 


CHAPTER    XXXIII. 

SCIENCE  OF  THE  NINETEENTH  CENTURY  (CONTINUED). 

History  of  Spectrum  Analysis — Discovery  of  Heat-rays  by  Sir  W. 
Herschel — And  of  Chemical  Rays  by  Ritter  of  Jena — Photo- 
graphy first  suggested  by  Davy  and  Wedgwood — Carried  out  by 
Daguerre  and  Talbot — Dark  Lines  in  the  Spectrum  first  ob- 
served by  WoUaston — Mapped  by  Fraunhofer — Life  of  Fraun- 
hofer — He  discovers  that  the  Dark  Lines  are  different  in  Sun- 
light and  Star-light — Experiments  on  the  Spectra  of  different 
Flames — Four  new  Metals  discovered  by  Spectrum  Analysis — 
Artificial  Dark  Lines  produced  in  the  Spectrum  by  Sir  David 
Brewster — Bunsen  and  Kirchhofif  explain  the  Dark  Lines  in  the 
Solar  Spectrum — Metals  in  the  Atmosphere  of  the  Sun — Huggins 
and  Miller  examine  the  Stars  and  Nebulae  by  Spectrum  Analysis  .  3  r5 


CONTENTS. 


CHAPTER    XXXIV. 

SCIENCE  OF  THE  NINETEENTH  CENTURY  (CONTINUED). 

PAGE 

Early  Theories  about  Heat — Count  Rumford  shows  that  Heat  can 
be  produced  by  Friction — He  makes  Water  boil  by  boring  a 
Cannon — Davy  makes  two  pieces  of  Ice  melt  by  Friction — His 
conclusion  about  Heat— How  'Latent  Heat'  is  explained  on 
the  theory  that  Heat  is  a  kind  of  Motion — Dr.  Mayer  suggests 
the  Determination  of  the  Mechanical  Equivalent  of  Heat — Dr. 
Joule's  Experiments  on  the  conversion  of  Motion  into  Heat — Dr. 
Him's  Experiments  on  the  conversion  of  Heat  into  Motion — Proof 
of  the  Indestructibility  of  Force  and  Conservation  of  Energy     .  329 

CHAPTER  XXXV. 

SCIENCE   OF  THE  NINETEENTH   CENTURY   ^CONTINUED). 

Oersted  discovers  the  Effect  of  Electricity  upon  a  Magnet — Electro- 
Magnetism — Experiments  by  Ampere  on  Magnetic  and  Electric 
Currents — Ampere's  Early  Life — Direction  of  the  North  Pole  of 
the  Magnet  depends  on  the  course  of  the  Electric  Currents — 
Magnetic  Currents  set  up  between  two  Electric  Wires — Electro- 
Magnets  made  by  means  of  an  Electric  Current — Arago  magne- 
tises a  Steel  Bar  with  an  ordinary  Electrical  Machine — Faraday 
discovers  the  Rotatory  Movement  of  Magnets  and  Electrified 
Wires — Produces  an  Electric  Current  by  means  of  a  Magnet — 
Seebeck  discovers  Thermo-Electricity,  or  the  production  of  Elec- 
tricity by  Heat — Schwabe  discovers  Periodicity  of  the  Spots  on 
the  Sun — Sabine  suggests  a  connection  between  Sun-spots  and 
Magnetic  Currents — This  proved  in  1859  by  Observations  of 
Carrington  and  Hodgson — Electric  Telegraph— Wheatstone — 
Cooke — Steinheil — Morse — Bain      ......   34.1 

CHAPTER    XXXVI. 

SCIENCE  OF  THE  NINETEENTH  CENTURY  (CONTINUED/. 

Davy  discovers  that  Nitrous  Oxide  produces  Insensibility — Laugh- 
ing-gas— Safety-lamp,  18 15 — Nicholson  and  Carlisle  discover 
Decomposition  of  Water,  1800 — Davy  discovers  the  effect  of 
Electricity  upon    Chemical   Affinity — Faraday's  Discoveries  in 


xxii  CONTENTS. 


FAGS 

Electrolysis — Indestructibility  of  Force — Various  Modes  dis- 
covered of  Decomposing  Substances — ^John  Dalton,  chemist — 
Law  of  Definite  Proportions — Law  of  Multiple  Proportions — 
Dalton's  Atomic  Theory — The  Study  of  Organic  Chemistry — 
Liebig,  the  great  teacher  in  Organic  Chemistry  .  .  .   362 

CHAPTER    XXXVn. 

SCIENCE   OF   THE   NINETEENTH   CENTURY    (CONTINUED). 

The  Organic  Sciences  are  too  difficult  to  follow  out  in  detail — . 
Jussieii's  Natural  System  of  Plants — Goethe  proves  the  Meta- 
morphosis of  Plants — Humboldt  studies  the  Lines  of  Average 
Temperature  on  the  Globe — Extends  our  knowledge  of  Physical 
Geography — Writes  the  '  Cosmos ' — Death  of  Humboldt  in 
1858 380 


CHAPTER    XXXVin. 

SCIENCE  OF  THE  NINETEENTH   CENTURY   (CONTINUED). 

The  three  Natui'alists,  Lamarck,  Cuvier,  and  Geoffroy  St.-Hilaire 
— Cuvier  begins  the  Museum  of  Comparative  Anatomy — La- 
marck's History  of  Invertebrate  Animals — G.  St.-Hilaire  brings 
Natural  History  Collections  from  Egypt — Lamarck  on  the 
Development  of  Animals — G.  St.-Hilaire  on  'Homology,'  or 
the  similarity  in  the  parts  of  different  animals — Cuvier's  '  Regne 
Animal '  and  his  Classification  of  Animals — Cuvier  on  the  Per- 
fect Agreement  between  the  Different  Parts  of  an  animal — He 
Studies  and  Restores  the  Remains  of  Fossil  Animals — His 
'  Ossemens  Fossiles  ' — Death  of  Cuvier — Von  Baer  on  the  Study 
of  Embryology — His  History  of  the  Development  of  Animals, 
1828 388 

CHAPTER  XXXIX. 

SCIENCE  OF  THE   NINETEENTH   CENTURY   (CONTINUED). 

Prejudices  which  retarded  the  study  of  Geology — Sir  Charles 
Lyell  traces  out  the  Changes  going  on  now — Mud  carried  down 
by  the  Ganges — Eating  away  of  Sea-coasts — Eruption  of  Skap- 
tar  Jokul — Earthquake  of  Calabria — Rise  and  Fall  of  Land — 


CONTENTS. 


PAGE 

•Principles  of  Geology'  published  in  1830 — Louis  Agassiz:  his 
early  life — De  Saussure's  Study  of  Glaciers — Agassiz  on  Europe 
and  North  America  being  once  covered  with  Ice — Boucher  de 
Perthes  on  Ancient  Flint  Implements — McEnery  on  Flint  Im- 
plements in  Kent's  Cavern,  v^dth  Bones  of  Extinct  Animals — 
Swiss  Lake-dwellings — '  Antiquity  of  Man '      ....   404 


CHAPTER   XL. 

SCIENCE  OF  THE  NINETEENTH   CENTURY   (CONTINUED). 

Facts  which  led  Naturalists  to  believe  that  the  different  kinds  of 
Animals  are  descended  from  Common  Ancestors — All  Animals  of 
each  class  formed  on  one  Plan — Embryological  Structure — 
Living  and  Fossil  Animals  of  a  country  resemble  each  other — 
Gradual  Succession  of  Animals  on  the  Globe — Links  between 
different  species — Darwin's  Theory  of  Natural  Selection — 
Wallace  worked  out  the  same  Theory  independently — Sketch  of 
the  Theory  of  Natural  Selection — Selection  of  Animals  by  Man — 
Selection  by  Natural  Causes — Difficulties  in  Natural  History 
which  are  explained  by  this  Theory — Foolish  Prejudices  against 
it — Concluding  Remarks  on  the  History  of  Science  .         .         -4^9 


A    SHORT    HISTORY 

OF 

NATURAL    SCIENCE. 


INTRODUCTION. 

As  THIS  little  work  is  to  be  a  history  of  Natural  Science, 
it  will  be  as  well  to  begin  by  trying  to  understand  what 
Science  is. 

The  word  itself  comes  from  scio^  I  know,  and  means 
simply  knowledge.  The  science  of  botany  is  therefore  the 
knowledge  of  plants  ;  and  the  science  of  astronomy,  the  know- 
ledge of  the  heavenly  bodies. 

But  now  comes  the  question,  What  kind  of  knowledge  is 
required  ?  You  might  be  able  to  tell  the  names  of  all  the 
plants  in  the  world,  and  of  all  the  stars  in  the  sky,  and  yet 
have  scarcely  any  real  knowledge  of  botany  or  astronomy. 
You  will  easily  understand  this  if  we  compare  it  with  some- 
thing you  meet  with  in  daily  life.  Suppose  I  took  you  into 
a  large  school  and  told  you  the  names  of  all  the  children 
there  ;  even  if  you  learnt  these  names  by  heart,  you  could 
not  say  you  knew  the  children,  or  anything  about  them, 
beyond  their  names.  One  might  be  ill-tempered,  another 
good-tempered ;  one  might  have  a  home  and  a  father  and 
2 


HISTORY  OF  SCIENCE. 


mother,  another  might  be  an  orphan  and  homeless,  and  you 
would  find  their  mere  names  of  no  use  to  you  if  you  wished 
to  choose  one  of  them  to  do  any  work,  or  to  be  your  friend 
and  companion.  For  this  you  would  want  to  learn  their 
character,  their  habits,  and  other  real  facts  about  them. 

Now  this  last  is  just  the  kind  of  knowledge  which  is 
required  in  science.  If,  besides  the  name  of  a  plant,  you 
know  its  different  parts,  the  shape  of  its  leaves,  the  number 
of  its  seeds,  and  how  they  are  arranged  in  the  seed-vessel, 
the  number  of  stamens  or  thread-like  bodies  in  the  middle 
of  the  flower,  the  number  and  colour  of  its  petals  or  flower- 
leaves,  and  many  other  points  like  these,  then  you  know 
something  of  structural  botany.  If  you  know,  besides,  how 
a  plant  takes  up  food,  how  it  breathes,  and  how  the  sunlight 
acts  upon  the  leaves  and  alters  the  juices  of  the  plant,  then 
you  know  something  of  the  life  of  the  plant,  ox  physiological 
botany.  If  you  know  where  the  plant  grows  best,  in  what 
soil,  in  what  climate,  and  in  what  countries,  then  you  know 
something  oi  geographical  botany  ;  and  if  your  knowledge  is 
accurate  and  carefully  learnt  it  is  real  science. 

By  this  you  will  see  that  science  means  not  merely  know- 
ledge, but  an  accurate  and  clear  knowledge  about  the  things 
which  we  see  around  us  in  the  universe.  In  the  present  day, 
people  are  beginning  to  teach  children  much  more  on  these 
subjects  than  they  did  forty  years  ago,  and  every  intelligent 
boy  or  girl  probably  knows  that  Astronomy  is  the  science  of 
the  sun,  stars,  and  planets;  Physics  and  Mechanics^  the 
sciences  which  teach  the  properties  of  bodies  and  their  laws 
of  motion  ;  Biology  the  science  of  life  ;  Geology  the  science 
of  the  earth,  teaching  us  how  the  different  rocks  have  been 
formed ;  and  Chemistry  the  science  which  treats  of  the 
materials  of  which  all  substances  are  made,  and  shows  the 


IJ^TROD  UCTION. 


changes  which  take  place  when  two  substances  act  upon  one 
another  so  as  to  make  a  new  substance. 

There  are  many  simple  books  written  now  to  explain 
these  sciences,  and  those  who  wish  can  read  these  books  and 
study  the  examples  and  experiments  given  in  them.  They 
tell  us  what  science  now  is,  and  the  explanations  given  by 
the  best  men  about  the  universe  in  which  we  live.  But  they 
do  not  tell  us  how  science  has  become  what  it  is,  and  it  is  this 
which  I  hope  to  tell  you  in  the  present  book. 

A  man  who  wishes  to  understand  a  steam-engine  can  do 
so  by  going  to  an  engineer  and  having  each  part  explained 
to  him  j  but  if  he  wishes  to  know  the  history  of  the  steam- 
engine  he  must  go  back  to  the  first  one  ever  made,  and 
study  each  new  improvement  as  it  arose.  And  so  if  we  go 
back  to  the  first  attempts  made  by  thoughtful  men  to  under- 
stand nature,  and  then  trace  up  step  by  step  the  knowledge 
gained  from  century  to  century,  we  shall  have  at  least  a  mere 
intelligent  understanding  of  that  which  is  taught  us  now. 
But  if  we  have  any  true  love  of  knowledge  we  shall  gain  far 
more  than  this  ;  for  in  studying  the  history  of  those  grand 
and  patient  men  who  often  spent  their  lives  and  made  great 
sacrifices  to  understand  the  works  of  God,  the  merest  child 
must  feel  how  noble  it  is  to  long  and  strive  after  truth. 

When  we  go  back  to  very  early  ages  we  do  not  find  that 
people  understood  much  of  what  we  now  call  science.  So 
long  as  men  were  chiefly  occupied  in  protecting  themselves 
against  other  savage  men  and  wild  beasts,  and  had  to 
struggle  very  hard  to  get  food  and  clothing,  they  had  very 
little  time  or  wish  to  study  nature.  Still  they  learnt  many 
things  which  were  necessary  for  their  life.  They  learnt,  for 
instance,  at  what  times  the  sun  rose  and  set,  for  upon  this 


HISTORY  OF  SCIENCE. 


their  day's  work  depended.  They  learnt  at  what  time  in  the 
month  the  moon  was  full,  so  that  they  could  see  their  way 
by  moonlight ;  and  they  remarked  very  early  the  times  when 
spring,  summer,  autumn,  and  winter  came  round,  because 
the  sowing  of  their  seeds  and  the  gathering  of  their  fruits 
depended  upon  these  seasons. 

In  this  way  we  find  that  as  far  back  as  history  goes  men 
have  always  had  some  knowledge  of  the  facts  of  nature ;  and 
those  nations,  hke  the  Egyptians  and  Chinese,  which  long 
ago  had  become  highly  civilized,  had  learnt  a  very  great 
deal,  and  must  probably  have  known  some  things  of  which 
we  are  still  ignorant. 

There  has  been  a  great  deal  written  about  the  science  of 
the  Chinese,  Indians,  and  Egyptians,  but  I  shall  not  tell  you 
anything  about  them  here,  because  their  knowledge  has  had 
very  little  to  do  with  the  science  which  has  come  down  to 
us,  and  it  would  besides  be  difficult  to  give  you  any  real  idea 
of  what  they  knew  without  writing  a  book  on  the  subject. 

We  will  start,  therefore,  with  the  Greeks,  at  the  time  when 
they  first  began  to  try  and  explain  some  of  the  natural 
events  which  they  saw  taking  place  every  day.  This  was 
about  the  year  700  B.C.,  when  Thales,  one  of  the  seven  wise 
men,  was  living,  and  you  will  see  in  the  next  chapter  that 
even  at  this  time,  when  Greece  was  famous  for  its  learning, 
the  people  had  still  some  very  strange  ideas  about  the 
working  of  the  universe. 


PART    I. 
SCIENCE    OF    THE    GREEKS 

FROM   B.C.    639   TO   A.D.    200 


Chief  Men  of  Science  among  the  Greeks^ 


e 

B.C. 

Thales  . 

About    640. 

Anaximander 

.     610, 

Pythagoras    . 

500. 

Anaxagoras  . 

499- 

Democritas   . 

•     459. 

Hippocrates  , 

.     420. 

Eudoxus 

,     406. 

Aristotle 

■     384. 

Theophrastus 

37t- 

Aristarchus   . 

350^ 

Euclid  . 

300. 

Archimedes  . 

287. 

Erasi  stratus  . 

? 

Herophilus    . 

? 

Eratosthenes 

276. 

Hipparchus  . 

160. 

Strabo  . 

50  to  A.D.   18. 

Ptolemy 

.         70. 

Galen  . 

.     131' 

CH.  I.  SCIENCE   OF  THE   GREEKS. 


CHAPTER    I. 

639  TO  470  B.C. 

Ignorance  of  the  Greeks  concerning  Nature — Ionian  School  of  Learning 
— Thales  discovers  the  Solstices  and  Equinoxes,  and  knows  that  the 
Moon  Reflects  the  Light  of  the  Sun — Anaximander  invents  a  Sun- 
dial— Discovers  the  Phases  of  the  Moon^-Makes  a  Map  of  the 
Ancient  World — Pythagoras  teaches  that  the  Earth  moves,  and-  that 
the  Morning  and  Evening  Star  are  the  same — He  studies  Geology, 
and  knows  that  Land  has  in  some  places  become  Sea — True  sayings 
of  Pythagoras  and  his  Followers  about  Geology. 

About  600  years  before  Christ  was  born,  the  Greeks  were 
the  most  learned  people  in  Europe.  They  were  naturally  a 
handsome  and  clever  race,  and  their  young  men  were 
trained  to  be  both  good  soldiers  and  good  scholars.  An 
English  boy,  if  he  could  be  carried  back  to  those  days, 
would  find  that  the  young  Greeks  could  read,  write,  draw, 
and  argue  as  well  as  himself,  and  probably  that  they  could 
leap,  wrestle,  and  run  far  better  than  himself  or  any  of  his 
schoolfellows. 

But  on  some  points  he  would  find  that  their  ideas  were 
very  strange.  If  he  spoke  to  them  of  the  woiid  as  a  round 
globe  they  would  stare  in  astonishment,  and  tell  him  that 
such  an  idea  was  absurd,  for  everyone  knew  that  the  world 
was  flat  with  the  sea  flowing  all  round  it.  If  he  asked  them, 
in  his  turn,  about  Mount  Etna,  they  would  surprise  him  by 
replying  that  the  god  Vulcan  had  his  smithy  underneath  the 
mountain,  where  he  was  forging  thunderbolts  for  Jove,  and 


SCIENCE   OF  THE   GREEKS.  pt.  i. 


that  Etna  was  the  chimney  of  his  forge.  But  if  he  spoke  of 
the  sun  as  a  globe  of  Hght,  they  would  turn  away  from  him 
in  horror  as  a  wicked  unbeliever  in  the  gods,  for  who  among 
the  Greeks  did  not  know  that  the  sun  was  the  god  Apollo, 
who  drove  his  chariot  every  day  across  the  sky  from  east  to 
west  ?  In  fact,  the  Greeks,  though  learned  and  brave,  were 
quite  ignorant  of  what  we  now  call  '  natural  knowledge ; ' 
they  did  not  know  that  the  rising  and  setting  of  the  sun, 
and  the  eruption  of  a  volcano,  are  things  which  happen  from 
natural  causes  ;  but  everything  which  was  not  done  by  man, 
they  thought  was  the  work  of  invisible  beings  or  gods. 

It  was  not  long,  however,  before  some  wise  men  began 
to  think  more  deeply  about  these  things.  You  will  have 
read  in  Grecian  history  how  the  Greeks,  after  the  taking  of 
Troy,  crossed  over  the  Hellespont  and  founded  colonies  on 
the  coast  of  Asia  Minor ;  one  of  the  largest  of  these  colonies 
was  called  Ionia,  and  the  lonians  became  famous  for  their 
learning  and  wisdom. 

Thales,  640. — Here  Thales,  one  of  the  seven  wise  men 
of  Greece,  was  born  at  Miletus,  about  640  B.C.  Thales 
travelled  in  Egypt,  and  learned  many  things  from  the 
Egyptians,  and  then  returned  to  his  own  land  and  founded 
a  school  of  learning.  He  was  the  first  Greek  who  studied 
astronomy,  and  although,  like  his  countrjnnen,  he  believed 
that  the  earth  was  flat  and  floated  on  the  water,  yet  he  made 
several  great  discoveries. 

The  Greeks  had  always  divided  their  year  into  two  parts 
only,  summer  and  winter,  but  Thales  discovered  that  there 
are  four  distinct  divisions  marked  out  by  the  sun.  He 
noticed  that  in  the  middle  of  winter  the  sun,  instead  of 
passing  overhead,  reached  at  mid-day  only  a  certain  low 
point  in  the  heavens,  and  then  began  to  set  again,  so  that 


CH.  I.  THALES—ANAXIMANDER,  9 

the  day  was  short  and  the  night  long.  This  went  on  for  a 
few  days,  and  because  the  sun  stood  at  the  same  height 
every  day,  the  name  of  winter  solstice^  or  sun-standing,  was 
given  to  these  days  in  the  middle  of  winter.  Afterwards  the 
sun  began  to  rise  a  very  little  higher  every  day,  till  in  three 
months,  when  winter  had  passed  away  and  the  plants  and 
trees  began  to  bud,  the  sun  took  exactly  twelve  hoiurs  to  pass 
across  the  sky  from  sunrise  to  sunset,  so  then  the  day  was 
twelve  hours  long,  and  the  night  also  twelve  hours ;  this  was 
called  the  spring  equi-nox^  or  equal  night,  meaning  that  the 
day  and  night  were  of  equal  length.  After  this  the  sun  still 
rose  higher  every  day,  and  in  three  months  more  stood  for 
some  days  nearly  overhead  at  mid-day,  thus  making  a  long 
journey  from  sunrise  to  sunset,  and  causing  the  day  to  be 
long  and  the  night  short.  This  was-  the  summer  solstice. 
Then  the  sun  began  to  rise  less  high  every  day,  and  in 
another  three  months  there  was  again  equal  day  and  equal 
night — the  autumn  equinox  had  arrived.  Finally,  in  another 
three  months,  the  shortest  day  arrived  again,  and  the  whole 
round  began  afresh.  This  was  how  Thales  marked  out  the 
solstices  and  the  equinoxes ;  we  still  call  them  by  the  same 
name  as  he  did,  and  you  may  watch  these  changes  of  the 
sun  in  the  sky  for  yourself. 

Thales  knew  that  the  sun  and  stars  were  not  gods,  and 
thought  they  were  made  of  some  fiery  substance  ;  he  knew 
also  that  the  moon  receives  its  light  from  the  sun  and  reflects 
it  like  a  looking-glass.  He  was  very  learned  in  mathematics, 
and  invented  several  problems  now  found  in  the  '  Elements 
of  Euclid.'  He  is  also  said  to  have  foretold  an  eclipse,  but 
this  is  probably  not  true,  as  it  requires  more  knowledge  than 
he  is  likely  to  have  had. 

Anaximander  of  Miletus,  610  b.c,  the  friend  of  Thales, 


lo  SCIENCE   OF  THE   GREEKS.  ft.  I. 

was  the  next  Greek  who  made  some  important  discoveries  in 
science.  He  invented  a  sun-dial,  by  making  a  flat  metal 
plate  with  the  hours  of  the  day  marked  upon  it  in  a  certain 
order,  so  that  a  large  pin,  or  style  as  it  is  called,  standing  in 
the  middle  of  the  plate,  cast  a  shadow  on  the  right  hour 
whenever  the  sun  shone  upon  it.  You  can  understand  that 
as  the  sun  is  low  down  in  the  morning  and  gradually  passes 
overhead  during  the  day,  it  will  cause  the  pin  to  throw  its 
shadow  in  a  different  direction  at  different  hours. 

In  this  way  Anaximander  taught  the  Greeks  to  measure 
the  time  of  day.  He  is  also  said  to  have  been  the  first  as- 
tronomer who  understood  why  we  see  the  bright  face  of  the 
moon  growing  from  a  crescent  to  a  full  moon  and  then  di- 
minishing again.  To  know  this  he  must  also  have  known 
that  the  moon  moves  round  the  earth  every  month.  You  can 
imitate  the  changes  of  the  moon  if  you  take  a  round  stone 
and  hold  it  just  above  your  head  between  you  and  the  suH; 
you  will  then  have  its  shady  side  towards  you;  pass  it  slowly 
round  your  head,  you  will  find  that  you  see  first  a  bright  edge 
appearing,  then  more  and  more  of  the  bright  side,  till  when 
the  stone  is  on  one  side  of  your  head  and  the  sun  the  other, 
you  will  see  the  whole  of  one  side  of  the  stone  reflecting  the 
sun's  light — this  is  a  full  moon.  Pass  it  on  slowly  round,  and 
you  will  see  this  bright  side  disappear  gradually  till  you 
bring  it  back  to  its  old  position  between  you  and  the  sun, 
when  it  will  be  again  dark.  This  is  what  the  moon  does 
every  month,  producing  what  are  called  the  phases  of  the 
moo7i.  Anaximander  also  made  a  map  of  the  world,  or  at 
least  of  as  much  of  it  as  was  known  in  his  time. 

Pythagoras,  one  of  the  most  celebrated  of  the  learned 
men  of  Greece,  is  the  next  who  tells  us  anything  about  science. 
The  time  and  place  of  his  birth  is  uncertain,  but  he  lived 


CH.  I.  •         PYTHAGORAS  ON  GEOLOGY.  ii 

somewhere  between  566  and  470  B.C.  He  travelled  in 
Egypt,  and  learnt  much  there,  and  afterwards  settled  at  Ta- 
rentum,  in  Italy,  where  he  founded  a  famous  sect  called  the 
Pythagoreans.  You  will  read  of  the  opinions  of  Pythagoras 
in  books  of  philosophy,  but  we  are  only  concerned  with  what 
he  taught  about  nature. 

He  was  the  first  to  assert  that  the  earth  was  not  fixed, 
but  moved  in  the  heavens,  but  he  did  not  know  that  it 
m'oves  round  the  sun.  He  also  discovered  that  the  evening 
and  morning  star  are  the  same  planet;  he  called  this  planet 
Eosphorus,  for  it  did  not  receive  the  name  of  Venus  till  some 
time  afterwards. 

Some  of  the  most  remarkable  truths  taught  by  Pytha-* 
goras  were  about  geology,  or  the  study  of  the  earth.  He 
noticed  that  seashells  were  sometimes  to  be  found  far  inland 
imbedded  in  solid  ground  in  a  way  that  showed  they  were 
not  brought  there  by  man.  Therefore,  he  argued  that  to 
bury  j<?<z-shells  in  the  rocks,  the  sea  must  once  have  been 
there.  He  had  also  probably  watched  the  sea  eating  away 
the  cliffs  on  the  shores  of  Italy,  as  you  may  see  it  doing 
now  on  the  shores  of  Norfolk  and  Suffolk ;  and  when  he 
was  in  Egypt  he  must  have  seen  the  Nile  carrying  mud  and 
laying  it  down  at  its  mouth,  or  delta,  to  form  new  land.  From 
all  these  and  other  observations  he,  and  his  pupils  who  fol- 
lowed him,  drew  some  very  true  conclusions  w^hich  are  given 
in  Ovid's  '■  Metamorphoses' : — 

1.  Solid  land  has  been  converted  into  sea. 

2.  Sea  has  been  changed  into  land.  Marine  shells  lie 
far  distant  from  the  deep. 

3.  Valleys  have  been  excavated  by  running  water,  and 
floods  have  washed  down  hills  into  the  sea. 

4.  Islands  have  been  joined  to  the  mainland  by  the 


12  SCIENCE   OF  THE   GREEKS,  pt.  i. 

growth  of  deltas  and  new  deposits,  as  in  the  case  of  Antissa 
joined  to  Lesbos,  Pharos  to  Egypt,  &c. 

5.  Peninsulas  have  been  divided  from  the  mainland  and 
have  become  islands,  as  Leucadia  ;  and  according  to  tradi  - 
tion  Sicily,  the  sea  having  carried  away  the  isthmus. 

6.  Land  has  been  submerged  by  earthquakes  ;  the  Gre- 
cian cities  of  Helice  and  Buris,  for  example,  are  to  be  seen 
under  the  sea,  with  their  walls  inclined. 

7.  There  are  streams  which  have  a  petrifying  power,  and 
convert  the  substances  which  they  touch  into  marble. 

8.  Volcanic  vents  shift  their  position  ;  there  was  a  time 
when  Etna  was  not  a  burning  mountain,  and  the  time  will 
come  when  it  will  cease  to  burn. 

These,  and  other  sentences  of  the  same  kind,  show  how 
carefully  Pythagoras  and  his  followers  must  have  observed 
nature,  for  the  changes  that  are  going  on  upon  the  earth  take 
place  so  very  slowly  that  it  is  only  by  very  careful  comparison 
that  we  can  prove  they  are  happening  at  all.  Pythagoras 
was  the  first  man  who  was  called  z.  philosopher,  or  lover  of 
wisdom.  He  made  many  discoveries  about  musical  notes, 
and  succeeded  in  stretching  strings  so  that  when  struck  they 
gave  the  right  notes  of  the  octave  in  succession. 


CH.  II.        ANAXAGORAS  STUDIES  THE  MOOJST.  13 


CHAPTER    II. 

499   TO    322    B.C. 

Anaxagoras  studies  the  Moon — Describes  Eclipses  of  the  Sun  and 
Moon — Is  Tried  and  Condemned  for  Denying  that  the  Sun  is  a 
God — Hippocrates  the  Father  of  Medicine — Separates  the  Office  of 
Priest  and  Doctor — Studies  the  Human  Body — Eudoxus  has  an 
Observatory — Makes  a  Map  of  the  Stars — Explains  the  Movements 
of  the  Planets — Democritus  Studies  the  Milky  Way — Aristotle  an 
Astronomer  and  Zoologist — Divides  Animals  into  Classes — Teaches  ■ 
that  there  is  a  Gradual  Succession  of  Animal  Life — Studies  the 
Difference  of  the  Life  in  Plants  and  Animals. 

Anaxagoras,  who  was  the  next  great  teacher  after  Pythagoras, 
was  bom  in  Ionia  about  499  B.C.,  but  he  went  when  quite 
young  to  Athens.  He  loved  to  study  nature  for  its  own 
sake,  and  was  once  heard  to  say  that  he  was  bom  to  con- 
template the  sun,  moon,  and  heavens.  Although  there  were 
no  telescopes  in  those  days,  he  managed  to  observe  that 
there  were  mountains,  plains,  and  valleys  in  the  moon.  He 
believed  it  to  be  a  second  earth,  perhaps  with  living  beings 
in  it.  He  did  not  know,  as  we  do  now,  that  the  moon  has 
no  atmosphere  round  it,  such  as  living  beings  like  ourselves 
require  in  order  to  breathe.  He  discovered  that  an  eclipse 
of  the  sun  is  caused  by  the  moon  coming  directly  between 
the  earth  and  the  sun,  and  an  eclipse  of  the  moon  by  the 
earth  coming  between  the  moon  and  the  sun.  "When  the 
moon  comes  exactly  between  our  earth  and  the  sun,  we 
see  the  moon's  dark  body  pass   over  the  sun,  so  as  to 


14  SCIENCE   OF  THE   GREEKS.  PT.  T. 

eclipse  or  shut  it  out;  and  when  our  earth  comes  exactly 
between  the  moon  and  the  sun  we  cut  off  the  sun's  hght 
from  the  moon,  and  see  our  own  shadow  passing  over  the 
moon's  face,  and  thus  we  ecUpse  the  moon. 

Anaxagoras  knew  that  the  planets  Jupiter,  Saturn,  Venus, 
Mars,  and  Mercury  move  in  the  heavens,  and  that  the  stars 
do  not  move.  He  believed  that  all  the  heavenly  bodies 
were  fiery  stones ;  the  sun  he  thought  was  a  huge  fiery  stone 
as  big  as  the  Peloponnesus.  He  was  the  first  scientific  man 
who  was  persecuted  for  declaring  boldly  what  he  believed 
to  be  the  truth.  The  Greeks  were  very  angry  with  him  for 
teaching  that  the  sun  was  not  a  god;  so  he  was  tried  at 
Athens,  when  quite  an  old  man,  and  condemned  to  death. 
His  friend  Pericles  pleaded  for  him,  and  the  sentence  was 
changed  to  a  fine  and  banishment,  and  he  retired  to  Lamp- 
sacus,  where  he  went  on  teaching  science  and  philosophy 
till  his  death. 

Anaxagoras  was  the  first  Greek  philosopher  who  taught 
that  there  must  be  one  Great  Intelligence  ruling  over  the 
universe.  So  that  the  Greeks  punished  as  an  atheist  the 
man  who  first  taught  them  of  a  Supreme  God.  This  ex- 
ample should  teach  us  to  be  very  careful  how  we  condemn 
the  opinions  of  others,  for  fear  that  we,  like  the  Greeks, 
should  think  another  wicked  only  because  his  thoughts  are 
nobler  than  we  can  understand. 

Hippocrates,  420. — While  Anaxagoras  was  studying  the 
heavens,  another  man,  born  about  420  B.C.  in  the  little 
island  of  Cos,  was  studying  men,  and  how  to  make  their 
lives  healthier  and  happier.  Hippocrates,  the  Father  of 
Medicine,  belonged  to  a  family  of  doctors  and  priests. 
The  Greeks  did  not  understand  that  illness  comes  to  us 
because  we  do  not  know  how  to  take  care  of  our  bodies. 


CH.  II.  HIPPOCRATES— ARISTOTLE.  15 

They  thought  that  every  illness  was  a  punishment  sent  be- 
cause one  of  their  gods  was  angry,  so  when  they  were  ill 
they  sent  a  present  to  the  temple  of  ^sculapius,  the  god  of 
medicine,  and  then  went  to  the  priests  of  ^sculapius  to 
cure  them.  The  ancestors  of  Hippocrates  were  all  priests  of 
^sculapius,  but  he  separated  himself  from  the  priesthood 
and  devoted  his  time  to  studying  the  human  body,  and  find- 
ing out  the  causes  of  disease.  He  studied  the  effect  that 
heat  and  cold  have  upon  us,  and  taught  physicians  to  pay 
attention  to  the  kind  of  food  given  to  sick  people,  and  espe- 
cially to  watch  carefully  in  sickness  for  the  critical  point 
when  the  fever  is  at  its  height.  He  wrote  many  learned 
works  on  the  human  body,  and  you  should  remember  his 
name  as  the  Founder  of  the  science  of  Medicine. 

Eudoxus,  406 — Democritus,  459. — The  next  great  astro- 
nomer after  Anaxagoras  was  called  Eudoxus.  He  was  born 
about  406  B.C.,  at  Cnidos,  in  Asia  Minor,  where  he  had  an 
observatory,  from  which  he  could  watch  the  heavens,  and 
by  this  means  he  made  a  map  of  all  the  stars  then  known. 
He  was  the  first  Greek  astronomer  who  explained  how  the 
planets  Jupiter,  &c.,  moved  round  in  the  heavens,  and  the 
time  at  which  they  would  appear  again  exactly  in  the  same 
place  as  before.  The  great  philosopher  Democritus,  of 
Abdera  (459  B.C.),  who  lived  about  the  same  time  as 
Eudoxus,  made  the  remarkable  guess  that  the  beautiful 
bright  band  called  the  'Milky  Way,'  which  stretches  every 
evening  right  across  the  sky,  is  composed  of  millions  of 
stars  scattered  like  dust  over  the  heavens. 

Aristotle, io8^  one  of  the  most  famous  philosophers  of 
Greece,  was  also  a  great  student  of  nature.  He  was  bom  at 
Stagira,  in  Thrace,  384  B.C.,  but  studied  at  Athens  under 
Plato,   and  afterwards  became  the  tutor  of  Alexander  the 


i6  SCIENCE   OF  THE   GREEKS.  PT.  I. 


Great.  Aristotle  did  much  for  astronomy,  by  collecting  and 
comparing  the  discoveries  of  the  astronomers  who  came 
before  him.  He  is  the  first  of  the  Greek  writers  who  states 
very  decidedly  that  the  earth  must  be  a  round  globe,  and 
he  discovered  an  eclipse,  or  occultation  as  it  is  termed  by 
astronomers,  of  the  planet  Mars  by  the  moon. 

But  the  best  scientific  work  of  Aristotle  was  his  study  of 
animals.  He  persuaded  Alexander  the  Great,  who  governed 
Greece  at  that  time,  to  employ  several  thousand  people  to 
collect  specimens  of  animals  in  all  parts  of  Europe  and  Asia 
and  to  send  them  to  Athens.  Here  Aristotle  examined 
them  and  arranged  them  under  difierent  classes  according 
to  their  organs,  or  difi"erent  parts  of  their  body,  and  the  man- 
ner in  which  they  used  them.  Many  of  Aristotle's  divisions 
of  the  animal  kingdom  are  still  in  use,  and  he  may  fairly  be 
called  the  Founder  of  Zoology.  He  pointed  out  that  we  can 
trace  an  unbroken  chain  from  the  lowest  plant  up  to  the 
highest  animal,  each  group  being  only  divided  from  the 
next  by  very  slight  difierences ;  nor  can  we  tell,  he  said, 
where  plants  end  and  animals  begin,  for  there  are  some 
forms  which  are  so  Hke  both  plants  and  animals  that  we 
cannot  decide  in  which  division  to  place  them. 

He  also  pointed  out  that  the  life  in  plants  is  much  lower 
than  in  animals,  for  if  you  cut  a  plant  into  pieces,  each  piece 
will  grow,  showing  that  the  parts  of  a  plant  are  simple  and 
do  not  depend  very  closely  upon  each  other.  But  an  ani- 
mal, and  especially  one  of  the  higher  animals,  is  a  most 
complicated  piece  of  machinery.  If  you  hurt  or  destroy  any 
of  the  most  important  parts  the  whole  body  dies,  and  if  you 
cut  off  any  part  whatever,  that  part  dies  as  soon  as  it  is  se- 
parated from  the  rest.  These  and  many  other  very  interest- 
ing facts  about  animals  are  to  be  found  in  Aristotle's  great 


CH.  II.    THEOPHRASTUS  THE  FIRST  BOTANIST.  17 

work  on  Natural  History,  which,  however,  you  must  remem- 
ber, was  only  one  out  of  many  great  works  written  by  him  on 
subjects  which  do  not  concern  us  here. 

Theophrastus,  371. — Among  the  pupils  of  Aristotle  was 
a  man  named  Theophrastus,  who  was  born  at  Eresus,  371 
B.C.  Theophrastus  devoted  himself  chiefly  to  the  study  of 
plants,  and  is  the  first  botanist  whose  name  has  been  handed 
down  to  us.  The  Greel?:s  understood  very  little  about 
plants  except  those  which  they  used  for  medicine ;  but  Theo- 
phrastus described  about  500  different  kinds  of  plants,  and 
divided  them  into  trees,  herbs,  and  shrubs.  We  know,  how- 
ever, very  little  about  his  writings. 


1 8  SCIENCE   OF  THE   GREEKS,  FT.  I. 


CHAPTER  IIL 

320    to    212    B.C. 

School  of  Science  at  Alexandria — The  Ecliptic  and  the  Zodiac — Greeks 
believed  that  the  Sun  moved  round  the  Earth — Aristarchus  knew 
that  it  was  the  Earth  which  moved — He  also  knew  of  the  Obliquity 
of  the  Ecliptic,  and  that  the  Seasons  are  caused  by  it — He  knew 
that  the  Earth  turns  daily  on  its  Axis — Euclid  discovers  that  Light 
travels  in  straight  lines  —  Archimedes  discovers  the  Lever  — 
Principle  of  the  Lever — Hiero's  Crown,  and  how  Archimedes  dis- 
covered the  principle  of  Specific  Gravity. 

While  Aristotle  was  studying  science  at  Athens,  the  Greeks 
under  Alexander  the  Great  were  making  great  conquests  in 
Egypt,  where  Alexander  founded  a  city  bearing  his  own 
name  on  the  shores  of  the  Mediterranean.  After  Alexan- 
der's death  this  city,  called  Alexandria,  fell  to  the  portion  of 
Ptolemy  Lagus,  one  of  Alexander's  generals,  who  was  suc- 
ceeded by  a  number  of  princes  of  the  same  name.  The 
Ptolemies  were  all  patrons  of  learning  and  science,  and  the 
school  of  Alexandria  became  one  of  the  most  famous  the 
world  has  ever  known.  By  this  time  the  Greeks  had  learnt 
many  astronomical  facts,  some  of  them  probably  from  the 
Egyptians.  They  had  traced  the  ecliptic,  or  the  sun's  appa- 
rent yearly  path  through  the  heavens,  and,  dividing  this  path 
into  twelve  parts,  they  called  each  division  by  the  name  of  a 
constellation  or  cluster  of  stars.  These  constellations  re- 
ceived most  of  them  the  names  of  animals,  and  therefore 
the  circle  of  the  twelve  constellations  was  called  the  Zodiac^ 


CH.  III.  SIGNS   OF  THE  ZODIAC.  19 

or  circle  of  animals.  The  names  of  the  twelve  signs  are  ; 
I.  Aries  J  the  Ram;  2.  Taio'us,  the  Bull;  3.  Gemini,  the 
Twins  j  4.  Cancer,  the  Crab  ;  5.  Leo,  the  Lion ;  6.  Virgo, 
the  Virgin  ;  7.  Libra,  the  Balance  ;  8.  Scorpio,  the  Scorpion; 
9.  Sagittarius,  the  Archer;  10.  Capricornus,  \he.  Goat;  11. 
Aquarius,  the  Water-bearer  ;  12.  Pisces,  the  Fishes. 

It  was  by  no  means  an  easy  thing  to  trace  the  sun's  path 
among  the  stars,  because  the  sun  and  the  stars  are  never  in 
sight  at  the  same  time,  so  they  were  obliged  to  notice  the 
constellations  as  they  appeared  close  to  the  sun  after  he  sank 
at  night  or  before  he  rose  in  the  morning.  These,  they  found, 
varied  a  little  each  night,  till  when  a  whole  year  had  passed 
away,  all  the  twelve  signs  had  been  in  turn  close  to  the  sun,  and 
the  round  began  again.  Thus  they  learnt  that  the  sun  passed 
over  each  of  the  twelve  signs  in  the  course  of  the  year ;  and 
they  thought  from  this  that  the  sun  travelled  round  the  sky 
while  the  earth  stood  still  in  the  middle.  We  know  now 
that  it  is  the  sun  which  stands  still  in  the  middle  while  the 
earth  moves  round,  and  it  is  worth  while  to  make  an  experi- 
ment to  see  how  the  Greeks  were  deceived. 

Put  twelve  chairs  round  in  a  circle  to  represent  the 
signs  of  the  Zodiac,  and  put  yourself  in  the  middle  for  a 
person  standing  on  the  earth.  Then  swing  a  ball  round  you 
just  on  a  level  with  the  chairs.  You  will  see  that  the  ball 
passes  between  you  and  each  chair  as  it  makes  a  circle  round 
you.  The  Greeks  believed .  that  the  sun  moved  round  in 
this  way  between  us  and  the  stars.  But  now  to  represent 
what  really  takes  place,  change  places  with  the  ball.  Hang 
the  ball  (the  sun)  up  in  the  middle  just  on  a  level  with  the 
chairs,  and  walk  round  it.  Keep  your  eye  fixed  on  the  ball, 
and  you  will  see  it  will  pass  between  you  and  each  chair, 
just  as  it  did  before.     The  effect  is  the  same,  though  it  is 


20  SCIENCE   OF  THE   GREEKS,  pt.  i. 


you  who  are  moving  this  time  and  not  the  ball.  Thus  the 
Greeks  made  the  same  mistake  which  a  child  does  in  a  rail- 
way train  when  he  thinks  the  houses  and  trees  are  flying 
past,  while  it  is  he  himself  who  is  moving. 

Aristarchus. — There  was,  however,  one  Greek  astrono- 
mer named  Aristarchus,  who  discovered  the  real  movement 
as  we  know  it  now.  Aristarchus  was  bom  in  Samos,  some 
time  in  the  third  century  before  Christ,  but  he  came  to 
Alexandria,  and  was  tutor  to  the  sons  of  one  of  the  Ptolemies. 
He  taught  that  the  sun  was  immovable  like  the  fixed  stars, 
and  that  it  was  the  earth  which  travelled  round  the  ecliptic. 
He  knew  also  that  our  earth  does  not  stand  quite  upright  in 
its  journey  round  the  sun,  but  that  a  line  drawn  through  the 
earth  from  the  north  to  the  south  pole  would  be  sloping  or 
oblique  to  the  ecliptic,  and  that  this  obliquity  is  the.  cause  of 
our  four  seasons. 

If  you  do  not  understand  this  you  can  work  it  out  with 
your  ball,  using  a  lamp  to  represent  the  sun.  First  draw  an 
ink-line  round  the  middle  of  your  ball  for  the  equator,  then 
put  your  finger  and  thumb  at  the  two  ends  of  the  ball  to  re- 
present the  two  poles.  Do  not  hold  the  ball  upright,  but 
bring  your  thumb  nearer  to  you  than  your  finger.  A  line 
drawn  through  the  ball  from  your  finger  to  your  thumb  will 
now  be  inclined,  and  will  represent  the  inclined  axis  of  the 
earth.  Now  look  at  the  light  and  shade  on  the  ball  :  the 
north  pole,  which  is  turned  towards  the  lamp,  will  be  in  full 
light,  and  will  have  the  long  days  of  summer  j  the  south  pole 
turned  towards  you  will  be  in  the  dark,  enduring  its  long 
winter  night  Pass  the  ball  on  to  your  right,  and  when  you 
have  gone  round  a  quarter  of  a  circle  the  poles  will  both 
have  equal  light,  and  the  southern  spring  and  northern 
autumn  have  arrived.  Pass  on  again,  and  at  the  next  quarter 


CH.  III.  ARISTARCHUS  AND  EUCLID.  21 

the  south  pole  will  be  in  summer  and  the  north  pole  in 
winter,  while  at  the  fourth  and  last  point  you  have  the 
northern  spring  and  the  southern  autumn.  This  was  what 
Aristarchus  discovered,  namely,  that  the  changing  seasons 
are  entirely  caused  by  the  earth  having  its  axis  (or  the  line 
from  pole  to  pole)  oblique  to  its  path  round  the  sun,  called 
the  ecliptic.     This  is  called  the  obliquity  of  the  ecliptic. 

Aristarchus  appears  also  to  have  been  the  first  Greek 
who  understood  that  day  and  night  were  caused  by  the 
earth  turning  round  on  its  axis  every  day.  If  the  Greeks 
had  understood  his  teaching,  especially  about  the  earth 
moving  round  the  sun,  they  would  have  made  much  more 
progress  in  astronomy.  But  no  one  believed  him,  and  more 
than  1700  years  passed  away  before  Copernicus,  of  whom 
you  will  read  in  chapter  ix.,  discovered  this  great  truth  over 
again.  This  Greek  theory  of  the  earth  moving  round  the 
sun  is  often  called  the  Pythagorean  system^  for  it  was  thought 
that  Pythagoras  taught  it;  but  we  have  seen  that,  though 
Pythagoras  knew  that  the  earth  moves,  he  did  not  believe 
that  it  went  round  the  sun. 

Euclid,  300.  We  must  not  pass  through  the  third 
century  before  Christ  without  mentioning  Euclid,  the  great 
mathematician  and  geometer,  who  collected  together  the 
problems  in  the  '  Elements  of  Euclid,'  known  to  every 
schoolboy.  He  was  born  at  Alexandria  about  300  B.C. 
His  works  are  too  difficult  for  us  to  examine,  and  the  only 
discovery  of  his  we  can  mention  is,  that  light  travels  in 
straight  lines  called  ^  rays.'  Thus,  if  you  look  at  a  sunbeam 
shining  across  a  dusty  room,  you  can  see  the  light  reflected 
in  a  straight  line  along  the  particles  of  dust,  and  if  you  let 
sunHght  through  a  hole  in  the  shutter  into  a  dark  room,  it 
will  light  up  a  spot  on  the  wall  or  floor  exactly  opposite  to 


22  SCIENCE   OF  THE   GREEKS.  PT.  I. 

the  sun — the  middle  of  the  sun,  the  middle  of  the  hole  in  the 
shutter,  and  the  middle  of  the  spot  of  light,  will  all  be  in  a 
straight  line. 

Archimedes,  287. — Another  famous  geometer,  Archi- 
medes of  Syracuse,  bom  287  B.C.,  lived  about  the  same 
time  as  Euclid.  He  studied  for  many  years  at  Alexan- 
dria, but  afterwards  returned  to  his  native  country.  One 
of  the  greatest  discoveries  made  by  Archimedes  was  that 
of  a  lever.  If  you  place  a  book  upright  on  the  table 
and  lay  a  ruler  or  any  flat  piece  of  wood  or  metal  across 
it,  you  will  find  there  is  one  point  at  which  the  ruler  will 
balance.  .When  you  have  balanced  it,  put  an  ounce  weight 
on  each  end  and  it  will  still  balance  at  the  same  point, 
which  is  called  the  fulcrum.  But  now  change  the  ounce 
at  one  end  for  a  weight  of  two  ounces ;  that  end  will  sink 
at  once,  and  to  make  it  balance  you  will  have  to  shift  the 
ruler  and  make  the  light  end  twice  as  long,  because  the 
heavy  end  has  twice  the  weight  upon  it.  Put  a  three  ounce, 
and  you  must  again  lengthen  the  light  end  to  three  times  the 
length  of  the  heavy  one.  You  may  go  on  doing  this  till  the 
heavy  end  is  quite  close  to  \k\&  fulcrum  or  resting-point  of  the 
ruler,  and  still  the  light  weight  will  balance  the  heavy  one. 

This  is  the  principle  of  the  lever,  and  it  is  of  great  use  in 
lif  tmg  weights.  A  heavy  block  of  stone  which  no  set  of  men 
could  lift  by  taking  hold  of  it  may  be  easily  raised  by 
fastening  it  to  the  short  end  of  a  lever,  and  then  the  weight 
of  the  men  at  the  end  of  the  long  arm  will  balance  it,  as  the 
one-ounce  weight  balances  the  four-ounce.  Archimedes  was 
so  delighted  when  he  made  this  discovery  that  he  is  said  to 
have  exclaimed  :  '  Give  me  a  place  on  which  to  stand,  and  I 
will  raise  the  world.' 

Another  remarkable  discovery  made  by  Archimedes  con' 


CH.  III.  HIERO'S   CROWN.  23 


cerns  the  weight  of  bodies  immersed  in  water.  Hiero,  king 
of  Syracuse,  had  given  a  lump  of  gold  to  be  made  into  a 
crown,  and  when  it  came  back  he  suspected  that  the  workmen 
had  kept  back  some  of  the  gold  and  had  made  up  the  weight 
by  adding  more  than  the  right  quantity  of  silver;  but  he  had 
no  means  of  proving  this,  because  they  had  made  it  weigh 
as  much  as  if  it  had  been  pure  gold.  Archimedes,  puzzling 
over  this  problem,  went  to  his  bath,  which  was  filled  to  the 
brim  with  water.  As  he  stepped  in  he  saw  the  water,  which 
his  body  displaced,  pouring  over  the  edge  of  the  bath,  and 
to  the  astonishment  of  his  servants  he  sprang  out  of  the  water 
and  ran  home  through  the  streets  of  Syracuse  almost  naked, 
crying  Eureka  !  Eureka  !  {'  I  have  found  it,  I  have  found  it.') 
What  had  he  found?  He  had  discovered  that  any 
solid  body  put  into  a  vessel  of  water  displaces  its  own  bulk 
of  water,  and  therefore,  if  the  sides  of  the  vessel  are  high 
enough  to  prevent  it  running  over,  the  water  will  rise  to  a 
certain  height.  He  now  got  one  ball  of  gold  and  another  of 
silver,  each  weighing  exactly  the  same  as  the  crown.  Of 
course  the  balls  were  not  the  same  size,  because  silver  is 
lighter  than  gold,  and  so  it  takes  more  of  it  to  make  the 
same  weight.  He  first  put  the  gold  ball  into  a  basin  of 
water,  and  marked  on  the  side  of  the  vessel  the  height  to 
which  the  water  rose.  Next,  taking  out  the  gold,  he  put  in 
the  silver  ball,  which,  though  it  weighed  the  same,  yet,  being 
larger,  made  the  water  rise  higher ;  and  this  height  he  also 
marked.  Lastly,  he  took  out  the  silver  ball  and  put  in  the 
crown.  Now,  if  the  crown  had  been  pure  gold,  the  water 
would  have  risen  only  up  to  the  mark  of  the  gold  ball,  but 
it  rose  higher  and  stood  between  the  gold  and  silver  mark, 
showing  that  silver  had  been  mixed  with  it,  making  it  more 
bulky.     This  was  the  first  attempt  to  measure  the  specific 


24 


SCIENCE   OF  THE   GREEKS. 


PT.  I. 


gravity  of  different  substances,  that  is,  the  weight  of  any- 
particular  substance  compared  to  an  equal  bulk  of  water. 

It  wiU  be  quite  sufficient  if  you  remember  the  experiment 
as  I  have  explained  it  j  but  as  you  may  perhaps  be  puzzled 
to  see  how  it  can  have  anything  to  do  with  weight,  you  can, 
if  you  wish,  try  to  master  the  following  explanation  of  Fig.  i, 

Fig.  I. 


0|~J                       0 

a       1  '^'^ 

,t                    5 

.:            5-F 

10 -p                           10 

10  -t 

c 

;                     : 

Brr-                                15 

..                       15-- 

Diagram  showing  the  difference  of  specific  gravity  between  equal  weights  of  gold, 

silver,  and  mixed  metal. 
ABC,  Spring  balances,     d.  Gold  ball  weighing  19  oz.     e.  Silver  ball  weighing  19  oz. 

f.  Crown  of  mixed  metal  weighing  19  oz. 

which  shows  how  specific  gravity  is  measured.  You  must 
begin  by  remembering  that  the  crown,  the  gold  ball,  and  the 
silver  ball,  when  weighed  in  the  air,  will  all  pull  the  marker  of 
the  spring  balances  a,  b,  c,  down  to  1 9  ;  that  is,  they  will  all 
weigh  19  ounces.    But  when  they  are  immersed  in  water  they 


CH.  III.        ARCHIMEDES— SPECIFIC  GRAVITY.  25 

will  no  longer  weigh  the  same,  because  the  water  round 
them  buoys  them  up  just  as  much  as  it  would  buoy  up  the 
quantity  of  water  which  they  displace. 

Now,  the  gold  ball  takes  the  place  of  as  much  water  as 
would  weigh  one  ounce  if  you  could  take  it  out  and  weigh  it 
in  the  air.  So  the  gold  ball  is  buoyed  up  one  ounce  by  the 
water  round  it,  and  accordingly  you  see  it  only  pulls  the 
marker  down  18  ounces  instead  of  19.  But  the  silver  ball, 
although  it  weighs  the  same,  is  larger,  and  takes  the  place  of 
nearly  two  ounces  of  water,  therefore  it  is  buoyed  up  nearly 
two  ounces,  and  only  pulls  the  marker  down  to  1 7.  Now,  as 
the  crown  weighs  the  same  as  the  two  balls,  its  shape  is  of 
no  consequence  ;  if  it  was  made  all  of  gold  it  would  take  as 
much  room,  and  be  buoyed  up  as  much  as  the  gold  bail.  If 
it  was  all  silver  it  would  be  buoyed  up  as  much  as  the  silver 
ball,  and  therefore,  as  it  pulls  the  marker  down  half-way 
between  17  and  18  ounces,  it  must  be  half  gold  and  half 
silver. 

In  this  way  Archimedes  showed  how  we  can  learn  the 
weight  of  any  substance  compared  to  an  equal  bulk  of  water, 
and  this  is  called  the  *  specific  gravity '  of  the  substance. 

He  also  invented  a  screw  for  pumping  up  water,  which  is 
still  called  the  'screw  of  Archimedes.' 

Archimedes  was  unfortunately  killed  in  the  city  of 
Syracuse  when  it  was  besieged  by  the  Romans  during  the 
second  Punic  war.  The  General  Maecenas  had  given  special 
orders  that  his  life  should  be  spared ;  but  he  was  so  deeply 
engaged  in  solving  a  problem  that  he  heard  nothing  of  the 
din  of  war  around  him,  and  a  common  soldier  not  being 
able  to  get  any  answer  from  him,  killed  him  without  knowing 
who  he  was. 


26  SCIENCE   OF  THE   GREEKS.  PT.  i. 


CHAPTER    IV. 

280  TO  120  B.C. 

Erasistratus  and  Herophilus  study  the  Human  Body — Eratosthenes  the 
Geographer  lays  down  the  First  Parallel  of  Latitude,  and  the  First 
Meridian  of  Longitude — He  measures  the  Circumference  of  the 
Earth — Hipparchus  writes  on  Astronomy — Catalogues  1,080  Stars 
— ^Calculates  when  Eclipses  will  take  place — Discovers  the  Pre- 
cession of  the  Equinoxes. 

Erasistratas  and  HeropMlus. — At  the  time  when  Archi- 
medes was  studying  in  Alexandria,  two  physicians  were 
teaching  there,  who  are  famous  in  the  history  of  anatomy^  or 
the  structure  of  the  body.  The  one  was  Erasistratus  and 
the  other  Herophilus.  The  birthplaces  and  dates  of  these 
two  physicians  are  doubtful,  but  we  know  that  they  were  the 
first  men  who  dissected  the  human  body,  and  gave  a  clear 
account  of  its  parts.  Erasistratus,  in  particular,  described 
the  brain  and  its  curious  windings  or  convolutions,  and  the 
division  between  the  cerebrum  or  front  part  and  the  cere- 
bellum or  hinder  and  lower  part.  He  seems  also  to  have 
known  that  it  is  in  our  brain  that  we  feel  everything,  and 
that  it  is  the  nerves  which  carry  messages  from  different 
parts  of  our  body  to  our  brain.  Herophilus  traced  out  the 
tendons  or  strong  cords  which  fasten  the  muscles  to  the 
bones,  the  ligaments  or  fibrous  cords  which  unite  one  bone 
to  another ;  and  the  nerves.  He  is  the  first  physician  who 
pointed  out  that  in  feeling  a  pulse  you  must  notice  three 


CH.  IV.  ERATOSTHENES— PARALLEL    OF  LATITUDE.  27 

things  :  ist,  how  strongly  it  throbs  j  2nd,  how  quickly;  3rd, 
whether  the  beats  are  regular  or  irregular.  Many  of  the 
names  which  Erasistratus  and  Herophilus  gave  to  parts  of  the 
body  are  still  used  by  anatomists,  and  the  school  of  medi- 
cine founded  by  them  in  Alexandria  was  renowned  for  more 
than  six  hundred  years. 

Eratosthenes,  276. — We  must  now  turn  to  the  science  of 
geography,  which  at  this  time  began  first  really  to  be  studied 
by  a  Greek  named  Eratosthenes,  born  at  Cyrene  276  b.c. 
Like  all  men  of  science  of  that  day,  he  too  came  to  Alex- 
andria, where  the  king,  Ptolemy  Evergetes,  made  him  keeper 
of  the  Royal  Library.  He  made  a  map  of  all  the  world  that 
was  then  known,  and  described  the  countries  of  Europe, 
Asia,  and  Libya.  But  his  two  great  works  were,  laying 
down  the  first  parallel  of  latitude,  and  trying  to  measure  the 
circumference  of  the  earth.  He  laid  down  the  parallel  of 
latitude  in  the  following  manner.  He  knew  that  at  all 
places  on  the  equator  the  day  was  exactly  the  same  length 
all  the  year  round,  and  that  the  length  of  the  days  and 
nights  varied  more  and  more  as  you  went  northwards; 
therefore  he  reasoned  that,  if  he  could  draw  a  line  east  and 
west  through  a  number  of  places  whose  longest  day  was 
exactly  the  same  length,  those  places  would  all  be  at  the 
same  distance  from  the  equator.  He  began  at  the  Straits  of 
Gibraltar,  where  the  longest  day  was  exactly  14 J  hours,  and 
then  observing  all  those  places  whose  longest  day  was  also 
14J  hours,  he  drew  a  line  through  the  south  coast  of  Sicily, 
across  the  south  of  the  Peloponnesus,  the  island  of  Rhodes, 
the  bay  of  Issus,  and  across  the  Euphrates  and  Tigris,  out 
to  the  mountains  of  India.  If  you  follow  this  line  on  a 
map  you  will  find  it  is  the  36th  parallel  of  north  latitude, 
and  that  Eratosthenes'  observation  was  perfectly  correct. 


28  SCIENCE   OF  THE    GREEKS.  PT.  I. 

This  discovery  led  him  on  to  try  and  measure  the  cir- 
cumference of  the  earth.  Having  found  a  line  straight 
round  the  earth  from  east  to  west,  he  knew  that  if  he  drew 
a  line  at  right  angles  to  it,  that  is  exactly  north  and  south, 
he  should  have  a  line  which  would  describe  a  circle  round 
the  earth  from  pole  to  pole,  as  the  equator  marks  a  circle 
round  the  earth  midway  between  the  two  poles.  This 
second  line  he  drew  from  Alexandria,  and  it  passed  right 
through  Syene,  now  called  Assouan,  one  of  the  southern 
cities  of  Egypt,  and  thus  he  knew  that  Alexandria  and 
Syene  were  on  the  same  meridian  of  longitude. 

Now  he  found  that  at  Syene  the  sun  was  exactly  over- 
head at  midday,  at  the  time  of  the  summer  solstice.  He 
knew  this  by  means  of  a  gnomon,  or  upright  pillar  (b,  Fig.  2), 
which  was  used  by  the  Greeks  to  measure  the  height  of  the 
sun  in  the  sky.  At  Syene  this  pillar  cast  no  shadow  at  noon 
of  the  summer  solstice,  proving  that  the  sun  shone  straight 
down  upon  the  top  of  it ;  and  this  was  further  proved  by  the 
sun  shining  down  to  the  bottom  of  a  deep  well,  which  it 
would  not  do  unless  it  were  directly  overhead.  But  at 
Alexandria  the  gnomon  did  cast  a  shadow,  because,  as 
Alexandria  was  further  north  and  the  earth  is  round,  the 
sun  there  was  not  directly  overhead.  Now,  as  light 
travels  in  straight  lines  (see  p.  21),  a  line  Urawn  from 
the  extreme  point  of  the  shadow  cast  by  the  pillar  or 
gnomon  up  to  the  top  of  the  pillar  itself  would,  if  carried 
on,  run  straight  into  the  sun,  and  thus  the  angle  between 
this  line  and  the  pillar  showed  at  what  angle  the  sun's  rays 
were  falling  at  Alexandria.  By  measuring  this  angle,  Eratos- 
thenes found  that  Alexandria  was  g'-g-th  of  the  whole  circum- 
ference of  the  earth  north  of  Syene,  where  the  rays  were 
perpendicular.  You  can  form  an  idea  of  this  from  the 
accompanying  diagram,  Fig.  2. 


CH.  IV.       CIRCUMFERENCE   OF  THE  EARTH. 


29 


Let  the  large  circle  represent  the  earth  ;  b  the  gnomon 
at  Syene,  and  a  the  gnomon  at  Alexandria.  The  length  of 
the  shadow  c  d  of  the  gnomon  a,  will  bear  the  same  pro- 
portion to  the  circumference  of  the  small  circle  (drawn  from 
the  top  of  the  gnomon  as 
a  centre),  that  the  distance 
from  Alexandria  to  Syene 
(d  to  e)  does  to  the  whole 
circumference  of  the  globe. 
This  is  true  only  if  the  rays 
from  the  sun  to  Alexandria 
and  to  Syene  are  parallel 
(or  run  at  equal  distances). 
They  are  not  really  quite 
parallel  because  they  meet 
in  the  sun,  but  Eratosthenes 
knew  that  the  sun  was  at 
such  an  enormous  distance 
that  their  approach  to  each 
other  was  quite  unimpor- 
tant. He  now  measured  the  distance  between  Alexandria 
and  Syene  and  found  it  to  be  5,000  stadia,  or  about  625 
miles,  and  multiplying  this  by  50  he  got  625  x  50  =  31,250 
miles  as  the  whole  circumference  of  the  earth,  measured 
round  from  pole  to  pole.  This  result  is  not  quite  correct, 
but  as  nearly  as  could  be  expected  from  a  first  rough 
attempt.  Eratosthenes  also  studied  the  direction  of  moun- 
tain-chains, the  way  in  which  clouds  carry  rain,  the  shape  of 
the  continents,  and  many  other  geographical  problems. 

HipparelLUS,  160.— Nearly  one  hundred  years  after 
Eratosthenes,  the  great  astronomer  Hipparchus  was  bom, 
160  B.C.     Hipparchus  was  the  most  famous  of  all  the  astro- 


Diagram  showing  how  Eratosthenes  mea- 
sured the  circumfelfence  of  the  earth. 

A,  Gnomon  at  Alexandria,  b,  Gnomon  at 
Syene.  c  d.  Length  ofshadow  of  gnomon. 
D  E,  Distance  from  Alexandria  to  Syene. 


30  SCIENCE   OF  THE   GREEKS.  pt.  r. 

nomers  who  lived  before  the  Christian  era.  He  collected 
and  examined  all  the  discoveries  made  by  the  earlier  obser- 
vers, and  made  many  new  observations  j  but  astronomy  had 
now  become  so  complicated  that  the  problems  are  too  diffi- 
cult to  be  explained  here.  Hipparchus  made  a  catalogue  of 
1, 08.0  stars,  and  showed  how  they  are  grouped  with  regard  to 
the  ecliptic.  He  also  calculated  accurately  when  eclipses  of 
the  sun  or  the  moon  would  take  place.  But  his  great  disco- 
very was  that  called  the  '  Precession  of  the  Equinoxes.'  This 
is  a  veiy  complicated  movement  which  you  can  only  under- 
stand by  reading  works  on  Astronomy  \  but  I  will  try  to  give 
a  rough  idea  of  it,  in  order  that  you  may  always  connect  it 
with  the  name  of  Hipparchus. 

We  have  seen  that  the  earth  has  two  movements — one, 
turning  on  its  own  axis  causing  day  and  night ;  the  other, 
travelling  round  the  sun,  causing  the  seasons  of  the  year. 
But  besides  these  it  has  a  third  curious  movement,  just  like 
a  spinning-top  when  it  is  going  to  fall.  Look  at  a  top  a 
little  while  before  it  falls,  and  you  will  see  that,  because  it  is 
leaning  sideways,  the  top  of  it  makes  a  small  circle  in  the 
air.  Now  our  earth,  because  it  is  pulled  at  the  equator  by 
the  sun,  moon,  and  planets,  makes  just  such  a  small  circle 
in  space  ;  so  that,  instead  of  the  north  pole  pointing  quite 
straight  to  the  polar  star,  it  makes  a  little  circuit  in  the 
sky,  with  the  polar  star  in  the  centre.  The  pole  moves 
very  slowly,  taking  twenty- one  thousand  years  to  go  all 
round  this  circle.  To  understand  the  effect  of  this  move- 
ment we  must  examine  more  closely  what  the  equinoxes 
are.  Take  your  ball  again  and  make  it  go  round  the  lamp 
with  its  axis  incHned  (see  p.  20).  When  you  have  it  in  such 
a  position  that  the  north  pole  is  in  the  dark,  or  the  northern 
winter  solstice,  you  will  find  that  a  straight  line  drawn  from 


en.  IV.  PRECESSION  OF  THE  EQUINOXES.  31 

the  sun  to  the  centre  of  the  earth  will  not  meet  the  equator 
but  a  point  to  the  south  of  it.  But  now  pass  the  ball  on  to 
the  next  point  when  neither  pole  is  in  shade,  and  when  it  is 
equal  day  and  equal  night  over  the  globe  (our  spring  equi- 
nox), a  line  now  drawn  from  the  sun  will  fall  directly  upon 
the  equator,  so  that  the  sun's  path  meets  the  equator  at 
this  point,  which  is  called  the  equinoctial  point.  Pass  on 
till  the  south  pole  of  your  ball  is  in  the  dark,  the  sun  will 
now  fall  directly  on  a  point  noiih  of  the  equator  (making  our 
summer  solstice).  Pass  on  again  to  the  point  of  equal  day 
and  equal  night,  and  the  sun  again  falls  direct  on  the  equa- 
tor, causing  our  autumn  equinox.^  _NoWj_if_theearth  did  not 
make  that  small  circlein_space_l  i  k  e  ^the  top,  the  sun  ^ould_ 
always  touch  the  equator^at  exactly  those  same  points  of 
the  eartTi's  <?r7//  or  path  round  the  sun;  but  the  effect  of 
That  movement  is  to  pull  the  equator  slightly  back,  so 
that  the  points  where  the  ecliptic  and  the  equator  cut 
each  other  are  5 of  seconds  more  to  the  west  every  year, 
and  in  this  way  the  equinoxes  travel  all  round  the  orbit 
from  east  to  west  in  21,000  years.  Hipparchus  discovered 
this  pre-cession  (or  going  forward)  of  the  equinoxes ;  though 
he  did  not  know,  what  Newton  afterwards  discovered,  that 
it  is  caused  by  the  sun  and  moon  pulling  at  the  mass  of 
extra  matter  which  is  gathered  round  the  equator. 


32  .     SCIENCE   OF  THE   GREEKS.  ft.  I. 


CHAPTER  V. 

FROM    A.D.    70    TO    200. 

Ptolemy  founds  the  Ptolemaic  System — He  writes  on  Geography — 
Strabo,  a  great  traveller,  -writes  on  Geography — Studies  Earth- 
quakes and  Volcanoes — Galen  the  greatest  Physician  of  Antiquity — 
Describes  the  Two  Sets  of  Nerves — Proves  that  Arteries  contain 
Blood  —  Lays  down  a  theory  of  Medicine  —  Greece  and  her 
Colonies  conquered  by  Rome — Decay  of  Science  in  Greece — Con- 
cluding remarks  on  Greek  Science. 

Ptolemy,  a.d.  70.— After  Hipparchus  there  were  many  good 
astronomers  at  Alexandria,  but  none  whom  we  need  notice 
until  the  year  70  after  Christ,  when  Ptolemy  Claudius,  a 
native  of  Egypt,  was  born.  He  was  not  one  of  the  Ptole- 
mies who  governed  Alexandria,  and  the  place  of  his  birth  is 
unknown,  but  he  is  famous  for  having  made  a  regular  system 
of  astronomy  founded  upon  all  that  the  Greeks  had  learnt 
about  the  heavens.  His  discoveries,  like  those  of  Hippar- 
chus, are  too  complicated  for  us  to  discuss  here ;  they  re- 
lated chiefly  to  the  movements  of  the  moon  and  the  planets; 
but  the  one  great  thing  to  be  remembered  of  him  is,_that  he 
jbunded  wJiaLis  .xall£Ld-,t;ha  JPtolemak  System  oi.  astronomjj^ 
^vhich  tries  to  explain  all  the  movements  of  the  sun,  stars, 
and  planets,  by  supposing  the  earth  to  stand  still  in  the 
centre  of  them  all.  This^stemJs^jiiitained-iiL-Ptolemy's 
great  work  caJlled_JJhe_Syntaxis/  may  seem  strange  that, 
as  it  is  not  true  that^the_earth  is_.tli£-.centre,_  Ptolemy  should 
have  been  able  to  explain  so  much  by  his  system,  but  you 


CH.  V.  PTOLEMY  AND  STRABO.  '  33 

must '  remember  that  it  had  the  same  effect  whether  you 
moved  roim3riKe^r]7"or" tlie^bal^tTound "yoii  iiTQur  experi- 
ment jm^gage.X9,X andPtole^  explanations  were  apparently 
^o  near  the  truth  that  astronomers  were  satisfied  with  them  for 
1,400  years,  till  Copernicus  discovered  the  real  movements. 

Ptolemy  was  a  geographer  as  well  as  an  astronomer ; 
he  wrote  a  book  on  geography  which  was  used  in  all  the 
schools  of  learning  for  nearly  fourteen  hundred  years.  He 
drew  maps  of  all  the  known  parts  of  the  world,  and  laid 
down  on  them  lines  of  latitude  and  longitude,  which  he  cal- 
culated by  the  rules  Eratosthenes  had  discovered.  In  his 
geography  he  describes  the  countries  from  the  Canary  Islands 
on  the  west  to  India  and  China  on  the  east,  and  from  Norway 
to  the  south  of  Egypt.  He  describes  our  island  under  the 
name  of  Albion,  or  Britain,  and  traces  out  many  of  the  coast- 
lines and  rivers.  He  also  gives  the  names  of  the  various 
towns,  with  their  latitude  and  longitude. 

Strabo.— A  little  before  the  time  of  Ptolemy  there  lived 
a  famous  traveller  named  Strabo,  who  wrote  a  great  deal  on 
geography.  He  was  born  at  Amasia,  in  Cappadocia,  and 
was  probably  living  when  Christ  was  born.  Strabo  in  his 
book  describes  the  countries  which  he  visited  and  read  about. 
He  also  studied  earthquakes  and  volcanoes,  and  pointed  out 
that,  when  the  hot  vapour  and  lava  hidden  in  the  crust  of 
our  earth  cannot  escape,  they  cause  earthquakes,  but  that 
when  they  find  their  way  out  through  a  volcano,  like  Etna,-, 
the  country  is  not  so  often  disturbed  and  shaken. 

Galen,  131. — There  is  still  one  more  great  man  of  science 
whom  we  must  mention  as  belonging  to  the  Greek  school  at 
Alexandria.  This  was  Galen,  one  of  the  most  celebrated 
physicians  of  antiquity.  He  was  born  a.d.  131,  at  Perga- 
mos,  in  Asia  Minor,  and  during  his  life  he  is  said  to  have 


34  SCIENCE    OF   THE   GREEKS.  PT.  i. 

written  more  than  500  valuable  essays  on  medicine  and  the 
human  body.  You  will  remember  that  Erasistratus  and 
Herophilus  dissected  the  human  body  j  but  in  the  time  of 
Galen  this  seems  to  have  been  forbidden,  and  he  was  obliged 
to  work  upon  monkeys  and  other  animals.  Even  from  these, 
however,  he  learnt  some  very  important  facts.  For  instance, 
he  discovered  the  difference  between  the  two  sets  of  nerves 
which  we  have  in  our  body,  called  the  nerves  of  sensation 
and  the  nerves  of  motion. 

Our  bodies  are  provided  with  two  sets  of  fine  cords  or 
threads  called  nerves ;  one  set  running  from  different  parts  of 
the  body  to  the  spine  and  the  brain,  and  the  other  set  run- 
ning back  from  the  spine  and  brain  to  the  body.  If  you 
touch  a  hot  iron  with  your  finger,  the  nerves  of  sensation, 
that  is,  of  feeling,  carry  the  message  to  your  brain  that 
the  iron  is  hot,  and  then  instantly  the  nerves  of  motion 
carry  the  message  back  from  your  brain  to  your  finger,  and 
you  snatch  it  away.  If  you  were  to  cut  the  nerves  of  your 
finger  you  would  not  feel  pain  nor  draw  your  finger  away. 
You  will  remember  that  Erasistratus  had  an  idea  that  it  is  in 
our  brain  that  we  feel ;  Galen  proved  this  by  many  experi- 
ments, though  he  did  not  understand  clearly  the  whole 
action  of  the  nerves.  He  also  proved  that  the  veins  of  our 
body  contain  blood,  and  he  described  the  two  muscles  which 
by  their  contraction  pull  down  the  lower  jaw  as  we  open 
^nd  pull  it  up  as  we  shut  our  mouths.  Besides  these  and 
many  other  discoveries,  Galen  worked  out  a  whole  theory  of 
medicine,  and  how  doctors  were  to  treat  their  patients,  and 
his  rules  were  the  guide  of  physicians  for  many  hundred 
years. 

Concluding  Remarks  on  Greek  Science. — V/e  have  now 
come  to  an  end  of  the  science  of  the  Greeks.     You  will 


CH.  V.  CONCLUDING  REMARKS.  35 

read  in  Grecian  history  how  Greece  and  the  Greek  colonies 
were  conquered  by- the  Romans  more  than  a  hundred  years 
before  Christ  was  born;  and  when  the  Greeks  ceased  to  be  a 
free  people  they  gradually  lost  their  love  of  discovery  and 
of  science.  The  school  at  Alexandria  continued  to  be 
famous  for  many  centuries  after  Christ,  but  the  professors 
who  taught  there  only  repeated  the  sayings  of  Ptolemy, 
Aristotle,  Galen,  and  the  other  great  discoverers,  and  did 
not  find  out  new  facts  for  themselves;  and  at  last,  in  the  year 
640  after  Christ,  the  Arabs  took  possession  of  the  city,  and 
it  soon  ceased  altogether  to  be  Greek. 

You  must  remember  that  in  these  five  chapters  we  have 
only  been  able  to  speak  of  some  of  the  greatest  men,  and 
then  only  of  a  few  of  the  discoveries  they  made.  You  will 
hear  of  many  celebrated  Greek  philosophers,  as,  for  example, 
Socrates  and  Plato,  whose  names  are  not  mentioned  here  be- 
cause they  wrote  on  subjects  such  as  the  mind  and  the  soul, 
which  belong  to  higher  philosophy,  and  not  to  Natural 
Science.  You  will  also  hear  of  many  strange  and  absurd 
notions  about  the  causes  of  things  which  in  those  early 
days  were  held,  even  by  such  men  as  Pythagoras  or  Galen ; 
but  in  this  book  we  have  only  to  try  to  understand  the  real 
facts  which  have  been  discovered  ;^and  there  is  no  doubt 
that  the  Greeks,  by  a  patient  study  of  nature,  and  by  making 
real  and  careful  observations  and  experiments,  laid  the 
foundation  of  much  of  the  knowledge  which  we  have  carried 
so  much  further  in  modem  times.  The  moment  they  began 
merely  to  repeat  the  teachings  of  others,  instead  of  trying 
and  proving  the  truth  of  them,  they  made  no  more  disco- 
veries, but  lost  a  great  deal  they  had  gained.  For  a  mere 
reading  of  books  will  not  teach  science  ;  and  if  you  admire 
these  men  for  making  great  discoveries,  and  would  like  to 


36  SCIENCE   OF  THE   GREEKS.  pt.  i. 

be  a  discoverer  yourself,  you  must  not  be  content  with 
knowing  what  has  been  done,  but  must  set  to  work  as  they 
did,  and  observe  and  make  experiments  for  yourself.  \ 


Chief  Works  consulted. — Draper's  'Intellectual  Development  in 
Europe  ; '  Lewis's  *  Astronomy  of  the  Ancients  ; '  '  Encyclopaedia  Bri- 
tannica,'  art.  'Astronomy  ;'  Herschel's  'Astronomy;'  Baden  Powell's 
'History  of  Natural  Philosophy;'  Lardner's  'Cyclopaedia,'  1834; 
Sprengel's  '  Histoire  de  la  Medecine,'  1815 ;  Grant's  '  History  of 
Physical  Astronomy ; '  Lange's  '  Geschichte  des  Materialismus  ; '  Rees's 
'Encyclopaedia;'  Whewell's  'History  of  Inductive  Sciences.' 


PART   IT. 

SCIENCE    OF    THE 
MIDDLE    OR    DARK    AGES 

FROM   A.D.    700   TO   A.D.    15QO 


Chief  Men  of  Science  in  the  Middle  Ages. 


Marcus  Grsecus 

Geber  or  Djafer 

Albategnuis 

Ben  Musa   . 

Avicenna     . 

Gerbert 

Ebn  Junis    . 

Alhazen 

Roger  Bacon 

Vitellio 

Flavio  Gioja 

Columbus    . 

Vasco  de  Gama 

Ferdinand  Magellan 

Leonardo  da  Vinci 


A.D. 

800. 
830. 

879. 

900. 

980. 
1000. 
1008. 
1000. 
1214. 
1220. 
1300. 

1435. 
1450. 

1470. 

1452. 


CH.  VI.  SCIENCE   OF  THE  ARABS.  39 


CHAPTER  VL 

SCIENCE    OF    THE   ARABS- 

Dark  Ages  of  Europe — Taking  of  Alexandria  by  the  Araos  and  burning 
of  the  Library — The  Arabs,  checked  in  their  conquests  by  Charles 
Martel,  settle  down  to  Science — The  Nestorians  and  Jews  trans- 
late Greek  Works  on  Science — Universities  of  the  Arabs — Chemistry 
first  studied  by  the  Arabs  —  Alchemy,  or  the  attempt  to  make 
Gold  —  Hermes  the  first  Alchemist  —  Hermetically-sealed  Tubes — 
Gases  and  Vapours  called  '  Spirits '  by  the  Arabs — The  use  of  this 
Word  retained  by  us. 

Arabian  Science. — We  have  now  arrived  at  what  have  been 
called  the  '  Dark  Ages/  because  for  several  hundred  years 
Europe  was  too  much  engaged  in  wars  and  disputes  to  pay- 
any  attention  to  learning  or  science.  You  have,  no  doubt, 
read  in  history  how  the  Goths  and  Vandals,  a  barbarous 
people  from  north-eastern  Asia,  spread  themselves  over 
Europe,  conquering  the  Romans,  and  taking  possession  of 
all  their  colonies.  They  even  crossed  over  into  Africa,  but 
were  driven  out  again  by  the  famous  General  Belisarius,  in 
the  reign  of  Justinian,  Emperor  of  Constantinople.  This 
was  in  the  year  a.d.  534,  and  the  Romans  held  Alexandria 
again  for  about  one  hundred  years,  and  then  came  the  Arabs 
or  Saracens,  pouring  out  of  Arabia,  and  they  took  posses- 
sion of  Alexandria  in  the  year  a.d.  639,  only  seven  years 
after  the  death  of  their  great  leader  Mahomet. 

The  first  thing  they  did  on  taking  the  city  was  to  burn 
the  famous  library  of  Alexandria,  and  it  seemed  as  if  they 


40  SCIEKCE   OF  THE  MIDDLE  AGES.  pt.  il. 

were  going  to  destroy  the  last  remnant  of  the  science  of  the 
Greeks.  But  it  proved  otherwise  :  they  went  on  conquering 
and  destroying  till  they  had  overrun  all  the  north  of  Africa 
up  to  the  Straits  of  Gibraltar,  had  taken  a  great  part  of  Spain 
and  even  of  the  south  of  France  as  far  as  the  river  Aude,  in 
Languedoc,  and  then  when  Charles  Martel,  mayor  of  the 
Franks,  conquered  them  at  Tours  in  732,  and  stopped  them 
from  going  any  farther,  they  settled  down  and  began  to  give 
their  attention  to  science  and  learning. 

They  found  in  Arabia  and  in  Egypt  two  classes  of  people 
who  were  able  to  teach  them  the  science  of  the  Greeks. 
These  were  the  Nestorians  and  the  Jews.  The  Nestorians, 
or  followers  of  Nestorius,  Bishop  of  Constantinople,  were  a 
peculiar  sect  of  Christians,  who  had  fled  into  Arabia  about 
the  year  450,  that  they  might  found  a  Church  of  their  own. 
They  became  very  powerful  and  learned,  and  translated 
many  of  the  Greek  works  of  science  into  the  Arabian 
language.  The  Jews,  after  the  fall  of  Jerusalem,  had  also 
taken  refuge  in  Syria  and  Mesopotamia,  and  they  were  very 
skilful  in  medicine,  and  founded  many  medical  colleges. 
The  Arabian  schools  of  Bagdad,  Cairo,  Salerno  in  the  south 
of  Italy,  and  Cordova  in  Spain,  soon  became  famous  all 
over  the  world.  The  Arabs  were  not  able  to  practise 
anatomy  in  their  medical  schools,  because  the  Koran,  that 
is  the  Mahommedan  Bible,  taught  that  it  was  not  right  to 
dissect  the  human  body,  so  they  turned  their  attention 
chiefly  to  medicine,  trying  to  discover  what  substances  they 
could  extract  from  plants  and  minerals,  at  first  to  serve  as 
medicines  but  soon  for  very  different  uses. 

Arabian  Alchemists. — They  found  something  in  the  old 
Greek  writings  about  the  way  to  melt  stones  or  minerals,  so 
as  to  get  out  of  them  iron,  mercury,  and  other  m.etals  ;  and 


CH.  VI,  ARABIAN  ALCHEMISTS.  41 

also  how  to  extract  many  beautiful  colours  out  of  rocks  and 
earths.  But  the  chief  thing  which  interested  them  in  the 
books  of  the  Egyptians,  Chaldeans,  and  Greeks,  was  the 
attempts  these  nations  had  made  to  turn  other  metals  into 
gold,  a  discovery  which  tradition  said  had  been  made  by  Her- 
■  mes  Trismegistus  about  2,000  years  before  Christ.  We  know 
very  little  of  this  Hermes,  and  indeed  we  are  not  sure 
whether  he  is  not  altogether  an  imaginary  person  ;  but  the 
alchemists,  as  the  people  were  called  who  tried  to  make  gold, 
considered  themselves  followers  of  Hermes,  and  often  called 
themselves  Hermetic  philosophers.  To  melt  the  mouth  of  a 
glass  tube  so  as  to  close  it  was  called  securing  it  with  '  Her- 
mes, his  seal,'  and  even  to  this  day  a  bottle  or  jar  which  is 
closed  so  that  it  is  air-tight  is  said  to  be  hermetically  sealed. 

The  Arabs  were  a  very  superstitious  people,  and  believed 
in  all  kinds  of  charms ;  and  this  idea  of  making  gold  in  a 
mysterious  way  took  a  great  hold  of  them.  Many  thousands 
of  clever  men  occupied  themselves  in  the  supposed  magic 
art  of  alchemy.  We  need  not  study  it  here,  but  only  observe 
how  very  useful  it  was  in  teaching  the  first  facts  of  chemistry. 
These  men,  who  were  many  of  them  learned,  clever,  and 
patient,  spent  their  lives  in  melting  up  different  substances 
and  watching  what  changes  took  place  in  them.  In  this 
way  they  learnt  a  great  deal  about  the  materials  of  which 
rocks,  minerals,  and  other  substances  are  made. 

One  of  the  first  things  they  discovered  was  that  by 
heating  some  substances,  such  as  nitre  or  saltpetre,  they 
drove  something  out  of  them  which  was  invisible,  and  yet 
that  they  could  collect  this  invisible  something  in  bottles; 
and  in  some  cases,  if  they  put  a  light  to  it,  it  exploded 
violently,  breaking  the  bottle  to  atoms.  Now,  because  this 
was  invisible  and  yet  so  powerful,  they  thought  it  must  be 


42  SCIENCE   OF  THE  MIDDLE  AGES.  pt.  ii. 

like  the  spirit  of  man,  which  can  do  so  much  and  yet  cannot 
be  seen,  and  for  this  reason  they  called  it  '  spirit/  We  know 
now  that  when  we  heat  substances  we  separate  part  of  the 
matter  of  which  they  are  made  into  very  small  portions, 
which  float  off  as  steam  or  gas  into  the  air;  so  that  this 
spirit  noticed  by  the  Arabs  was  vapour  or  gas. 

It  seems  almost  certain  that  the  Arabs  knew  a  great  deal 
about  gunpowder  and  some  other  mixtures  which  explode 
when  they  are  set  on  fire.  An  Arab  named  Marcus  Grsecus, 
who  lived  about  the  beginning  of  the  ninth  century,  says  that 
if  you  mix  together  one  pound  of  sulphur,  two  of  charcoal, 
and  six  of  saltpetre,  it  will  explode  when  you  light  it  -and 
drive  things  into  the  air.  This  is  one  of  the  ways  in  which 
gimpowder  is  still  made. 


CH.  VII.  CHEMISTRY  OF  GEBER.  43 


CHAPTER  VII. 

SCIENCE    OF    THE    ARABS    (CONTINUED). 

Geber,  or  Djafer,  the  founder  of  Chemistry — His  Explanation  of  Dis- 
tillation— Of  Sublimation — Discovers  that  some  Metals  increase  in 
weight  when  heated — Discovers  strong  Acids — Nitric  Acid — 
Sulphuric  Acid — Discovery  of  Sal-Ammoniac  by  the  Arabs — Arabs 
mix  up  Astronomy  with  Astrology — Albategnuis  calculates  the 
Length  of  the  Year — Mohammed  Ben  Musa,  first  writer  on  Algebra 
— Uses  the  Indian  Numerals — Gerbert  introduces  them  into  Europe 
— Alhazen's  discoveries  in  Optics — His  Explanation  why  only  one 
image  of  each  object  reaches  the  Brain — His  discovery  of  Refrac- 
tion, and  of  its  effect  on  the  light  of  the  Sun,  Moon,  and  Stars — His 
discovery  of  the  magnifying  power  of  rounded  glasses. 

Geber' s  discoveries  in  Chemistry,  800-900.— The  greatest 
of  the  Arabian  alchemists  was  a  man  named  Geber,  or 
Djafer,  who  was  born  in  Mesopotamia  about  a.d.  830. 
He  has  been  called  the  *  Founder  of  Chemistry,'  for  though, 
like  his  countrymen,  he  spent  much  of  his  time  in  trying  to 
make  gold,  yet  he  is  the  first  who,  as  far  as  we  know,  made 
really  useful  chemical  experiments. 

He  explains  in  his  works  many  of  the  methods  we  now 
use  in  chemistry.  For  example,  he  states  that  if  you  boil 
water,  the  vapour  (or  spirit  as  he  calls  it)  will  rise  up,  and 
you  can  collect  it  and  cool  it  down  again  in  another  vessel  j 
and  it  will  then  be  pure,  because  any  solid  matter  such  as 
sand  or  salt,  which  does  not  turn  readily  into  vapour,  will 
remain  behind  in  the  first  vessel.    Again,  if  you  heat  wine  or 


44  SCIENCE   OF  THE  MIDDLE  AGES.  pt.  ii. 


brandj  gently,  a  vapour  called  alcohol  or  spirits  of  wine  will 
rise  up,  because  the  alcohol  turns  into  vapour  more  easily 
than  the  other  materials  of  the  wine.  If  you  collect  and  cool 
down  this  vapour  in  another  bottle,  you  will  have  the  liquid 
spirits- of- wine.  This  process  is  called  distillatioti,  and  is 
used  by  chemists  to  separate  substances  which  turn  readily 
into  vapour  from  others  which  do  not  boil  so  easily.  You 
can  distil  vapours  from  solid  things  as  well  as  from  liquids  : 
if  you  heat  sugar  over  a  fire,  it  will  soon  boil,  and  a  vapour 
will  rise  up  from  it. 

But  if  you  put  a  piece  of  camphor  in  a  flask  with  a 
stopper  to  it,  and  heat  it  very  gently  either  by  placing  it  in 
the  sun  or  at  some  distance  above  a  lighted  candle,  the  cam- 
phor will  gradually  disappear  from  the  bottom  of  the  flask, 
and  collect  in  little  crystals  on  the  inside  of  the  neck.  This 
is  because  camphor  at  an  ordinary  heat  changes  straight  into 
a  dry  invisible  gas,  without  first,  becoming  liquid  as  ice  does. 
The  process  by  which  substances  are  turned  directly  from 
a  solid  state  into  a  dry  gas  is  called  sublimation,  and  Gefer 
describes  it  in  his  book  as  '  the  elevation  of  dry  things  by 
fire.'  He  knew  that  if  you  take  a  kind  of  stone  called 
cinnabar,  and  heat  it,  a  dry  gas  rises  from  it,  which  you  can 
collect,  and  which  cools  do\\Ti  into  drops  of  mercury  or 
quicksilver. 

Geber  made  another  remarkable  experiment,  though  he 
did  not  thoroughly  understand  it.  He  states  in  his  book 
that  if  you  take  a  certain  weight,  say  a  pound,  of  iron,  lead, 
or  copper,  and  heat  it  in  an  open  vessel,  the  metal  will  weigh 
more  after  it  has  been  heated  than  it  did  before,  which 
seems  very  strange,  as  we  cannot  see  that  anything  has  been 
added  to  it.  We  shall  learn  the  reason  of  this  when  we 
come  to  the  discoveries  of  Priestley  (chap,  xxvii.) ;  but  Geber 


CH.  VII.  GEBER  DISCOVERS  ACIDS,  45 

carefully  noticed  the  fact,  though  he  could  not  explain  it. 
But  the  discovery  which  most  of  all  gives  Geber  the  right  to 
be  called  the  '  founder  of  chemistry '  was  that  of  strong 
acids.  Most  of  the  chemical  experiments  we  make  now 
v/ould  be  impossible  without  acids,  but  before  Geber's  time 
vinegar  seems  to  have  been  the  strongest  acid  known.  He 
found,  however,  that  by  heating  copperas  (or  sulphate  of 
iron)  with  saltpetre  and  alum,  he  could  distil  off  a  vapour 
which  cooled  down  into  a  very  strong  acid,  now  called 
nitric  acid.  He  used  this  to  dissolve  silver,  and  by  mixing 
it  with  sal-ammoniac  he  found  it  would  even  dissolve  gold. 
Sal-amm9niac  was  a  kind  of  salt  which  was  known  to  the 
Arabs  before  Geber's  time.  They  made  it  by  heating  the 
dung  of  camels,  and  the  name  ammoniac  was  given  to  it 
because  they  made  it  first  in  the  desert  near  the  temple  of 
Jupiter  Ammon.  Geber  also  made  stdphuric  acid  by  dis- 
tilling alum.  When  we  remember  that  all  these  experiments 
were  made  more  than  a  thousand  years  ago,  we  must 
acknowledge  that  Geber  deserves  great  honour  for  the  dis- 
coveries which  he  made. 

Albategnuis,  879. — We  have  seen  that  in  chemistry  the 
Arabs  learned  very  little  from  the  Greeks,  but  in  mathe- 
matics and  astronomy  they  found  a  great  deal  written,  and 
the  Arabian  astronqmers  spent  much  of  their  time  in  trans- 
lating Greek  works.  Unfortunately  they  mixed  up  astronomy, 
or  the  study  of  the  heavenly  bodies,  with  astrology,  a  kind  of 
magic  art,  by  which  they  imagined  they  could  foretell  what 
was  going  to  happen  by  studying  the  stars.  In  spite  of  this, 
however,  there  were  several  very  celebrated  Arabian  astro- 
nomers, one  of  whom,  called  Albategnuis,  born  a.d.  879, 
made  a  great  many  good  observations.  He  calculated  the 
length  of  the  year  more  exactly  than  Ptolemy  had  done, 


46  SCIENCE   OF  THE  MIDDLE  AGES.  PT.  II. 

making  it  365  days,  5  hours,  46  minutes,  24  seconds,  which 
was  only  two  minutes  shorter  than  it  really  is,  and  he  cor- 
rected many  more  of  Ptolemy's  observations.  After  him 
the  next  famous  Arabian  astronomer  was  Ebn  Junis, 
A.D.  1008,  who  drew  up  several  valuable  astronomical 
tables. 

Ben  Musa,  900. — Of  mathematicians,  one  of  the  most 
celebrated  was  Mohammed  Ben  Musa,  who  lived  about 
A.D.  900.  He  is  the  earliest  Arabian  writer  on  algebra, 
or  the  working  of  sums  by  means  of  letters.  This  name 
*  Algebra '  is  an  Arabian  word,  and  the  Arabs  were  very 
clever  at  this  way  of  making  calculations.  Ben  ^  Musa  is 
the  first  writer  we  know  of  who  used  the  Indian  numerals 
I,  2,  3,  4,  5,  6,  7,  8,  9,  o,  instead  of  the  clumsy  Roman  nu- 
merals I,  II,  III,  IV,  &c.  If  you  try  to  do  a  sum  with  the 
Roman  numerals  you  will  see  what  a  troublesome  business 
it  is  and  what  a  great  gain  the  Indian  numerals  are.  The 
Arabs  learned  these  numbers  from  the  Hindoos,  and  always 
used  them  after  the  time  of  Ben  Musa,  so  that  they  are  now 
generally  called  the  Arabic  numerals.  About  the  year  1000. 
a  Frenchman  named  Gerbert,  Archbishop  of  Rheims,  and 
afterwards  Pope  Sylvester  the  Second,  who  had  been  edu- 
cated at  the  famous  Arabian  University  of  Cordova  in 
Spain,  introduced  them  into  Europe.  The  word  cipher. 
which  we  use  for  o,  comes  from  an  Arabic  word,  ctphra. 
meaning  empty  or  void. 

Alhazen's  discoveries  in  Optics,  1000. — Another  Arabian 
whom  we  must  specially  mention  was  an  astronomer  and 
mathematician  named  Alhazen,  who  was  born  at  Bassora,  in 
Asiatic  Turkey,  about  the  year  a.d.  iooo,  but  who  spent 
most  of  his  life  in  Spain.  He  made  discoveries  chiefly  in 
optics,  or  the  science  of  sight.    He  was  the  first  to  teach  that 


CH.  VII.  ALHAZEN  ON  REFRACTION.  47 

we  see  things  because  rays  of  light  from  the  objects  around 
us  strike  upon  the  retina  or  thin  membrane  of  our  eye,  and 
the  impression  is  carried  to  our  brain  by  a  nerve.  When 
the  object  is  itseh'  a  light,  like  the  flame  of  a  candle,  it  gives 
out  the  rays  which  reach  our  eye  ;  but  when,  like  a  book  or  a 
chair,  it  is  not  luminous,  then  the  rays  of  the  sun  or  any 
other  light-giving  body  are  reflected  from  it  to  our  eye  and 
make  a  picture  there.  Alhazen  also  explained  why  we  do 
not  see  two  pictures  of  one  object  although  we  look  at  it 
with  two  eyes  ;  he  pointed  out  that,  as  the  reflection  of  any 
given  point  of  the  object  is  formed  on  the  same  part  of  the 
one  eye  as  of  the  other,  only  one  united  picture  reaches  the 
brain.  This  is  the  best  explanation  which  has  ever  been 
given  of  why  we  only  see  one  image,  but  even  to  this  day  we 
are  not  quite  certain  that  it  is  satisfactory. 

Alhazen  discovered  another  wonderful  thing  about  light. 
If  you  take  a  straight  stick  and  hold 
it  in  a  slanting  direction  in  a  basin 
of  water  so  that  half  of  it  is  under   '^'\X 
water,  the  stick  will  appear  to  bend  N. 

at  the  point  a,  where  it  touches  ^^^ 

the  surface   of  the   water,  and   in-  \i^^^^^0^ 

stead   of   going  along    the  dotted  ^^^^^^^ 

line  to  B,  will  look   as   if  it  went 

to  the  point  c.  This  is  because  rays  of  light  are  bent  in  a 
slanting  or  oblique  direction  when  they  pass  through  sub- 
stances of  different  density.  Water  is  more  dense  than  air, 
and  therefore  the  rays  of  light  reflected  from  the  stick  are 
bent  as  they  pass  out  of  the  water  into  the  air  on  their  way 
to  your  eye.  This  is  called  refraction^  or  the  breaking-back 
of  a  ray,  and  the  discovery  of  it  led  Alhazen  to  find  the 
explanation  of  a  very  curious  natural  fact. 


48 


SCIENCE   OF  THE  MIDDLE  AGES. 


PT.  II. 


He  knew  that  the  air  round  our  globe  grows  denser  as  it 
gets  nearer  the  earth,  so  he  argued  that  the  slanting  rays 
from  the  sun,  moon,  and  stars  must  become  bent  as  they 
approach  the  earth  and  pass  through  the  denser  air.  This, 
he  said,  causes  us  to  see  the  sun  after  it  has  really  sunk 
below  our  horizon  at  night,  and  before  it  rises  in  the 
morning  ;  for  the  rays  are  gradually  curved  by  passing 
through  the  denser  air  round  our  earth.    Fig.  4  explains  this. 

Fig.  4. 


Eartn 

Bending  of  the  Sun's  rays  by  the  atmosphere. 

s.  Sun.     s  c  and  s  v>,  Rays  as  they  would   travel  if  there  were   no   atmosphere. 
'    s  B  A,  Ray  bent  so  that  the  sun  becomes  visible  at  A. 

Supposing  the  sun  to  be  at  s,  and  a  person  at  a,  it  is  clear 
that  any  straight  ray  from  the  sun,  such  as  s  d,  could  not 
reach  A,  because  part  of  the  earth  is  in  the  way;  neither 
could  a  ray,  s  c,  reach  the  earth,  because  it  would  pass 
above  it.  But  when  the  rays  from  s  to  C  strike  the  at- 
mosphere at  B,  they  are  bent  out  of  their  course,  and  are 
gradually  curved  more  and  more  by  the  denser  air  till  they 
are  brought  down  to  the  earth  at  a,  and  so  the  sun  becomes 
visible. 

Alhazen  was  also  the  first  to  remark  that  a  convex  lens, 
that  is,  a  glass  with  rounded  surfaces,  such  as  our  common 
magnifying  glasses  and  burning  glasses,  will  make  things 
appear  larger  if  held  at  a  proper  distance  between  the  eve 


CH.  VII. 


ALHAZEN— MAGNIFYING   GLASSES. 


49 


and  any  object,  because  the  two  surfaces  of  the  glass,  be- 
coming more  and  more  oblique  to  each  other  as  they 
approach  the  sides,  bend  the  rays  inwards,  so  that  they  come 


Fig.  5. 


A 


B 


Arrow  magnified  by  a  convex  lens. 


to  a  focus  in  the  eye.  To  understand  this,  draw  a  line  of 
any  kind,  say  a  little  arrow,  on  a  sheet  of  paper,  and  bring 
your  eye  near  to  it.  Your  arrow  being  so  close  would 
look  very  large  if  you  could  see  it  distinctly,  but  just  be- 
cause it  is  so  near,  your  eye  cannot  focus  or  collect  together 
the  rays  coming  from  it  so  as  to  make  a  picture  on  the 
retina  at  the  back  of  the  eye ;  therefore  you  see  nothing 
but  an  indistinct  blur.  But  now  take  a  magnifying  glass, 
c  D,  fig.  5,  and  hold  it  between  your  eye  and  the  arrow.  If 
you  hold  it  at  the  right  distance  you  will  now  see  the  arrow 
distinctly,  because  the  greater  part  of  the  rays  have  been 
bent  or  refi-acted  by  the  rounded  glass  so  as  to  come  into 
focus  on  your  retina.  But  now  comes  another  curious  fact. 
It  is  a  law  of  sight,  that  when  rays  of  light  enter  our  eye  we 
follow  them  out  in  straight  lines,  however  much  they  may 
have  been  bent  in  coming  to  the  eye.  So  your  arrow  will 
not  appear  to  you  as  if  it  were  at  a  b,  but,  following  out  the 
dotted  lines,  you  will  see  a  magnified  arrow,  A  b,  at  the 


I 


50  SCIENCE   OF  THE   MIDDLE  AGES.  pt.  ii. 

distance  at  which  you  usually  see  small  objects  distinctly. 
This  observation  of  Alhazen's  about  the  bending  inwards  or 
converging  of  rays  through  rounded  glasses  was  the  first  step 
towards  spectacles. 

Besides  the  Arabians  whom  I  have  mentioned  here, 
there  were  many  who  were  very  celebrated,  but  we  know 
very  little  of  their  works.  Among  them  was  Avicenna 
A.D.  980,  whom  you  will  often  hear  mentioned  as  a  writer  on 
minerals.  But  the  chief  thing  to  be  remembered,  besides 
the  discoveries  of  Geber  and  Altiazen,  and  the  introduction 
of  the  Indian  numerals,  is  that  in  the  Dark  Ages,  when  all 
Europe  seemed  to  care  only  for  wars  and  idle  disputes,  it 
was  the  Arabs  who  kept  the  lamp  of  knowledge  alight  and 
patiently  led  the  way  to  modern  discoveries. 


CH.  VIII.  ROGER  BACON.  51 


CHAPTER  VIII. 

SCIENCE    OF   THE   MIDDLE   AGES  (CONTINUED). 

Roger  Bacon — His  '  Opus  Majus ' — His  Explanation  of  the  Rainbow  — 
He  makes  Gunpowder — Studies  Gases — Proves  a  Candle  will  not 
burn  without  Air — His  Description  of  a  Telescope — Speaks  of 
Ships  going  without  Sails— Flavio  Gioja  invents  the  Mariner's 
Compass — Greeks  knew  of  the  Power  of  the  Loadstone  to  attract 
Iron  —  Use  of  the  Compass  in  discovering  new  lands  —  Invention 
of  Printing — Columbus  discovers  America — Vasco  de  Gama  sees 
the  Stars  of  the  Southern  Hemisphere — Magellan's  ship  sails 
round  the  World — Inventions  of  Leonai'do  da  Vinci, 

We  must  now  return  to  Europe,  where  the  nations  were 
struggling  out  of  the  Dark  Ages;  and  though  there  were 
many  learned  men  in  the  monasteries,  very  few  of  them  paid 
any  attention  to  science :  while  those  who  did,  often  lost  their 
time  in  alchemy,  trying  to  make  gold  j  or  in  astrology,  pre- 
tending to  foretell  events  by  the  stars. 

Roger  Bacon,  1214. — In  the  year  12 14,  however,  a  man 
was  born  in  England  whom  every  Englishman  ought  to 
admire  and  revere,  because  in  those  benighted  times  he  gave 
up  his  whole  life  to  the  study  of  the  works  of  nature,  and 
suffered  imprisonment  in  the  cause  of  science.  This  was 
Roger  Bacon,  a  great  alchemist,  who  was  born  at  Ilchester 
in  Somersetshire,  educated  at  Oxford  and  Paris,  and  then 
became  a  friar  of  the  order  of  St.  Francis.  For  this  reason 
he  is  often  called  Friar  Bacon.  Bacon's  great  work,  called 
the  '  Opus  Majus,'  is  written  in  such  strange  language  that  it 


52  SCIENCE   OF  THE  MIDDLE  AGES.  pt.  ir. 


is  oftQji  difficult  to  find  out  how  much  he  really  knew  and 
how  much  he  only  guessed  at.  We  know,  however,  that  he 
made  many  good  astronomical  observations,  and  that  he 
explained  the  rainbow  by  saying  that  the  sun's  rays  are 
refiracted  or  bent  back  by  the  falling  drops  of  rain,  as 
was  also  noticed  about  the  same  time  by  Vitellio,  a  Polish 
philosopher. 

Bacon  is  famous  as  the  first  man  in  Europe  who  made 
gimpowder  ;  we  do  not  know  whether  he  learnt  the  method 
from  the  Arabs,  but  it  is  most  likely,  for  he  gives  the  same 
receipt  for  making  it  as  Marcus  Gr^ecus  did — namely,  salt- 
petre, charcoal,  and  sulphur.  He  also  knew  that  there  are 
different  kinds  of  gas,  or  air  as  he  calls  it,  and  he  tells  us 
that  one  of  these  puts  out  a  flame.  He  invented  the 
favourite  schoolboy's  experiment  of  burning  a  candle  under 
a  bell-glass  to  prove  that  when  the  air  is  exhausted  the 
candle  goes  out. 

Bacon  seems  also  to  have  known  the  theory  of  a  tele- 
scope. We  do  not  know  whether  he  ever  made  one,  but  he 
certainly  understood  how  valuable  it  would  be.  This  is 
what  he  says  about  it  in  his  '  Opus  Majus,'  or  '  Great  Work ' : 
*  We  can  place  transparent  bodies  (that  is,  glasses)  in  such  a 
form  and  position  between  our  eyes  and  other  objects  that 
the  rays  shall  be  refracted  and  bent  towards  any  place  we 
please,  so  that  we  shall  see  the  object  near  at  hand,  or  at  a 
distance,  under  any  angle  we  please  ;  and  thus  from  an  in- 
credible distance  we  may  read  the  smallest  letter,  and  may 
number  the  smallest  particles  of  sand,  by  reason  of  the  great- 
ness of  the  angle  under  which  they  appear.'  This  is  at  least 
a  very  fair  description  of  a  telescope.  In  the  same  book  he 
says  that  one  day  ships  will  go  on  the  water  without  sails, 
and   carriages  run  on  the  roads  without  horses,  and  that 


CH.  VIII.     I^LAVIO  GIOJA—MARINER'S   COMPASS.  ^^ 

people  will  make  machines  to  fly  in  the  air.  This  shows 
that  he  must  have  imagined  many  things  which  were  not 
really  discovered  till  more  than  300  years  afterwards  ;  but 
they  were  all  dreams  which  he  could  not  carry  out  himself. 
Before  we  leave  Roger  Bacon  I  must  warn  you  not  to  con- 
fuse him  with  Francis  Bacon,  Chancellor  of  England,  who 
was  quite  a  different  man,  and  lived  more  than  200  years 
later. 

Flavio  Gioja  discovers  the  Mariner's  Compass,  1300. — 
About  ten  years  after  the  death  of  Bacon,  a  man  was  born  in 
a  little  village  called  Amalfi,  near  Naples,  who  made  a  dis- 
covery of  great  value.  The  man's  name  was  Flavio  Gioja, 
and  the  discovery  was  that  of  the  viai'iner's  compass.  Long 
before  Flavio's  time  people  knew  that  there  was  a  kind  of 
stone  to  be  found  in  the  earth  which  attracted  iron.  There 
is  an  old  story  that  this  stone  was  first  discovered  by  a 
shepherd,  who,  while  resting,  laid  down  his  iron  shepherd's 
crook  by  his  side  on  a  hill,  and  when  he  tried  to  lift  it  again 
it  stuck  to  the  rock.  Although  this  story  is  probably  only  a 
legend,  yet  it  is  certain  that  the  Greeks  and  most  of  the 
ancient  nations  knew  that  the  loadstone  attracted  iron  ;  and 
a  piece  of  loadstone  is  called  a  magnet^  from  the  Greek  word 
magnes,  because  it  was  supposed  to  have  been  first  found  at 
Magnesia,.m  Ionia. 

A  piece  of  iron  rubbed  on  a  loadstone  becomes  itself  a 
magnet,  and  will  attract  other  pieces  of  iron.  But  Flavio 
Gioja  discovered  a  new  peculiarity  in  a  piece  of  magnetised 
iron,  which  led  to  his  making  the  mariner's  compass.  He 
found  that  if  a  needle  or  piece  of  iron  which  has  been 
magnetised  is  hung  by  its  middle  from  a  piece  of  light 
string,  it  will  always  turn  so  that  one  end  points  to  the 
north  and  the  other  to  the  south.     He   therefore   took  a 


54  SCIENCE   OF  THE  MIDDLE  AGES.  pt.  ir. 

piece  of  round  card,  and  marking  it  with  north,  south,  east, 

and  west,  he  fastened  a  magnetised  needle  upon  it  pointing 

Fig.  6.  from  N.  to  s.  j  he  then  fastened 

^^^^^^^^^^r~~--t  the  card  on  a  piece  of  cork 

;:^^^^B%— E— ^^^g\        ^^^  floated   it  in  a  basin  of 

^^^^^^T^iiL^^]]       water.      Whichever    w^ay    he 

^^^^^^^^^^  turned  the  card  round  till  the 

^^^^^  N.  of  the  needle    pointed  to 

Flavio's  Compass  floating  on  water.         ^^^    ^^^^^^    ^^^    ^^^    ^^    ^^    ^^^ 

south,  and  from  the  other  marks  on  the  card  he  could  then 
tell  the  direction  of  the  west,  north-west,  &c. 

You  will  see  at  once  how  important  this  discovery  was  ; 
for  when  a  ship  is  at  sea,  far  from  land,  there  is  nothing  to 
guide  the  captain  except  the  stars,  and  they  cannot  always 
be  seen,  so  that  before  he  had  a  compass  he  was  obliged  to 
•keep  in  sight  of  land  in  order  to  find  his  way.  But  as  soon 
as  he  had  an  instrument  which  pointed  out  to  him  which 
way  his  ship  was  going,  he  could  steer  boldly  and  safely 
right  across  the  sea. 

There  has  been  much  dispute  as  to  who  first  discovered 
the  compass,  and  some  people  think  that  the  Chinese  used  it 
in  very  early  times  ;  but  learned  men  now  agree  that  Gioja 
discovered  it  independently,  and  it  is  certain  that  he  was  the 
first  to  use  it  in  a  ship.  Of  course  it  would  have  been  very 
inconvenient  to  have  it  always  floating  in  a  basin  of  water ; 
so  the  card  was  fitted,  by  means  of  a  little  cap,  on  to  the  top 
of  a  pin,  round  which  it  could  turn  easily,  and  this  is  the  way 
it  is  still  made.  As  the  king  of  Naples  belonged  at  that 
time  to  the  royal  family  of  France,  Gioja  marked  the  north 
point  of  the  needle  with  a  fleur-de-lys  in  his  honour,  and  the 
mariner's  compass  of  all  nations  still  bears  this  mark.     The 


CH.  VIII.  INVENTION  OF  PRINTING.  55 

territory  of  Principiato,  where  Gioja  was  born,  has  also  a 
compass  for  its  arms,  in  memory  of  his  discovery. 

Invention  of  Printing,  1438. — Before  we  go  on  to  speak 
of  the  wonderful  voyages  which  followed  the  invention  of  the 
compass,  we  must  pause  a  moment  to  notice  another  great 
change  which  took  place  about  a  hundred  years  after  the 
time  of  Bacon  and  Gioja.  This  was  the  invention  of 
printing,  in  the  year  1438.  In  the  early  part  of  the  fifteenth 
century  some  people  began  to  engrave,  that  is,  to  cut  on 
wood,  pictures  and  texts  of  Scripture,  and  then  to  rub  them 
over  with  ink,  and  take  an  impression  of  them  on  paper. 
One  day  it  occurred  to  a  man  named  John  Gutenberg,  of 
Strasburg,  that  if  the  letters  of  a  text  could  be  made  each 
one  separate,  they  might  be  used  over  and  over  again.  He 
began  to  try  to  make  such  letters,  and  with  the  help  of  John . 
Faust  of  Mayence,  and  Peter  Schoeffer  of  Gernsheim,  both 
of  them  working  mechanics  like  himself,  he  succeeded  in 
making  metal  letters,  or  types  as  they  are  called.  These 
men  finished  printing  the  first  Bible  in  the  year  1455.  In 
1465  the  first  printing-press  was  started  in  Italy,  and  another 
in  Paris  in  1469,  while  Caxton  introduced  printing  into 
England  in  1474. 

It  is  easy  to  see  what  a  great  step  this  invention  was 
towards  new  knowledge.  So  long  as  people  were  obliged  to 
write  out  copies  of  every  work,  new  books  could  only  spread 
very  slowly,  and  old  books  were  very  dear  and  rare  \  but  as 
soon  as  hundreds  of  copies  could  be  printed  off  and  sold  in 
one  year,  the  works  of  the  Greeks  on  science  were  collected 
and  published  by  clever  men,  and  were  much  more  read 
than  before  ;  and  what  was  still  more  important,  books 
about  new  discoveries  passed  quickly  from  one  country  to 
another,  and  those  who  were  studying  new  truths  were  able 


56  SCIENCE   OF  THE  MIDDLE  AGES.  pt.  ii. 

to  learn  what  other  scientific  men  were  also  doing.  Thus 
printing  was  one  of  the  first  steps  out  of  the  ignorance  of  the 
Dark  Ages. 

Voyages  round  the  World. — The  next  step,  as  I  said 
just  now,  was  made  by  the  use  of  the  mariner's  compass. 
The  Greeks,  as  you  will  remember,  knew  that  the  earth  was 
a  globe,  but  all  this  had  been  forgotten  in  Europe  since  the 
Goths  and  Vandals  came  in,  and  people  actually  went  back 
to  the  old  idea  that  the  world  was  flat  like  a  dinner-plate, 
with  the  heavens  in  an  arch  overhead.  Nevertheless,  the 
sailors,  who  saw  ships  dip  down  and  disappear  gradually 
as  they  sailed  over  the  sea,  could  not  help  suspecting  that  it 
must  be  a  round  globe  after  all ;  and  Christopher  Columbus, 
a  native  of  Genoa,  was  convinced  he  could  find  a  way  round 
to  the  East  Indies  by  sailing  to  the  west  across  the  Atlantic. 
Full  of  this  idea,  he  started  on  August  3,  1492,  with  three 
small  ships  and  ninety  men,  from  Palos,  near  Cadiz,  in 
Spain,  and  sailed  first  to  the  Canary  Islands.  From  there  he 
sailed  on  for  three  weeks,  guided  by  his  compass,  but  with- 
out seeing  any  land;  the  food  in  the  ship  began  to  run 
short,  and  his  men  became  frightened  and  threatened  to 
throw  him  overboard  if  he  would  not  turn  back;  but  he 
begged  them  to  continue  for  three  days  longer,  and  a  little 
before  midnight  on  October  1 1  there  was  a  cry  of  '  land  ! 
land  ! '  and  next  morning  at  sunrise  they  disembarked  on  one 
of  the  Bahama  Islands  in  the  New  World. 

Columbus  thought  that  he  had  sailed  right  round  and 
reached  the  other  side  of  Asia,  but  if  you  look  at  your  map 
you  will  see  he  only  went  a  quarter  of  that  distance.  He  died 
in  1506,  without  finding  out  his  mistake,  though  he  made 
several  other  voyages.  During  these  he  made  a  very  remark- 
able discovery  about  the  magnetic  needle  of  the  compass.    It 


CH.  VIII.         VOYAGES  ROUND   THE   WORLD.  57 

had  long  been  known  that  the  needle  did  not  point  due 
north,  but  a  little  to  the  east  of  the  north.  Columbus,  how- 
ever, found  that,  as  he  went  westward,  the  needle  gradually 
lost  its  eastward  direction,  and  pointed  due  north,  and  then 
gradually  went  a  little  way  to  the  west.  It  remained  like 
this  till,  on  his  return,  he  came  back  to  the  same  place  where 
it  had  changed,  and  then  it  passed  gradually  back  to  its  first 
position.  From  this  he  learnt  that,  although  the  magnetic 
needle  always  points  towards  the  north,  it  varies  a  little  in 
different  parts  of  the  world.  The  reason  of  this  is  not  even 
now  clearly  understood,  and  we  must  content  ourselves  here 
with  knowing  that  it  is  so.  % 

The  next  grand  voyage  of  discovery  was  made  by  Vasco 
de  Gama,  a  Portuguese,  who  set  sail  July  9,  1497,  to  try 
whether  it  was  possible  to  sail  round  the  south  of  Africa. 
He  succeeded,  and  during  the  voyage  he  could  not  help 
remarking  the  new  constellations  or  groups  of  stars,  never 
seen  in  Portugal,  which  appeared  in  the  heavens.  This 
proved  to  him  that  the  earth  must  certainly  be  a  globe,  for  if 
you  were  to  sail  for  ever  round  a  flat  surface,  you  would 
always  have  the  same  stars  above  your  head. 

At  last  there  came  a  third  discoverer,  Ferdinand  Magellan 
(or  Magalhaens),  of  Spain,  who  set  off  August  10,  15 19,  deter- 
mined to  sail  right  round  the  world.  He  steered  westward 
to  South  America,  and  discovered  the  Straits  which  separate 
Terra  del  Fuego  from  the  mainland,  and  which  were  called 
after  him  the  Straits  of  Magellan.  Then  he  sailed  north- 
wards, across  the  equator  again,  till  he  came  to  the  Ladrone 
Islands,  where  he  was  killed  fighting  a  battle  to  help  the 
native  king.  Sebastian  del  Cano,  his  lieutenant,  then  took 
the  command  of  the  ship,  which  arrived  safely  back  in  the 
port  of  St.  Lucar,  near  Seville  in  Spain,  on  September  7, 


58  SCIENCE   OF  THE  MIDDLE  AGES.  pt.  il 

1522.  This  ship,  guided  by  Magellan,  was  the  first  which 
ever  sailed  quite  round  the  world  j  and  all  these  voyages, 
proving  that  the  earth  is  a  round  globe,  and  bringing  back 
accounts  of  new  stars  in  the  heavens,  set  men  thinking  that 
there  was  much  still  to  be  learnt  about  the  universe. 

Leonardo  da  Vinci,  1452. — We  must  not  pass  on  into 
the  sixteenth  century  without  mentioning  Leonardo  da 
Vinci,  the  great  painter,  who  was  also  very  remarkable  for 
the  number  of  interesting  inventions  which  he  made  in 
mechanics.  Leonardo  was  bom  in  1452  at  Vinci,  in 
Tuscany ;  he  is  so  generally  spoken  of  as  a  painter  that 
many^  people  do  not  know  that  he  left  behind  him  fourteen 
valuable  works  on  Natural  Philosophy.  He  invented  water- 
mills  and  water-engines,  as  well  as  locks  to  shut  off  the 
water,  such  as  are  now  used  on  our  canals  and  rivers.  He 
studied  the  flight  of  birds,  and  tried  to  make  a  machine  for 
flying,  and,  besides  being  one  of  the  best  engineers  of  his 
day,  he  made  many  curious  machines,  such  as  a  spinning- 
machine,  a  water-pump,  and  a  planing-machine.  Some  of 
these  things  were  only  models  which  he  made  for  his  own 
pleasure,  but  they  show  that  he,  like  Roger  Bacon,  was  very 
much  in  advance  of  his  age ;  and  he  did  good  service  to 
science  by  the  careful  experiments  which  he  made,  and  by 
insisting  that  it  was  only  by  going  to  Nature  herself  that  men 
can  really  advance  in  knowledge. 


Chief  Works  consulted. — Draper's  'Hist,  of  Intellectual  Develop- 
ment;' Baden  Powell's  '  Hist,  of  Natural  Philosophy,' 1834;  Sprengel 
*  Histoire  de  la  Medecine,'  1850  ;  '  Penny  Cyclopaedia,'  art.  'Arabians  ;' 
'Encyclopaedias  Metropolitana  and  Britannica;'  Rodwell's  'Birth  of 
Chemistry,'  1874;  'The  Works  of  Geber,'  Englished  by  R.  Russell, 


CH.  yiii.       SCIENCE   OF  THE  MIDDLE  AGES.  59 

1678;  Whewell's  'History  of  the  Inductive  Sciences;'  Priestley's 
'History  of  Vision,'  1772  ;  Smith's  'Optics,'  1778;  '  Edinburgh  En- 
cyclopaedia,' art.  Chemistry  J  Bacon's  'Opus  Majus,'  by  Dr.  Jebb, 
1733;  Bacon,  *  Sa  Vie,  ses  Ouvrages,  et  ses  Doctrines,'  by  M. 
Charles,  1861  ;  Ventura,  '  Ouvrages  Physico-mathematiques  de  Leon- 
ardo da  Vinci,'  1797;  Draper's  'Conflict  between  Religion  and 
Science,'  1875. 


PART    III. 

RISE    AND    PROGRESS    OF 
MODERN    SCIENCE 

FROM  A.D.  1500  TO  THE  PRESENT  DAY 


Chief  Scientific  Men  of  the  Sixteenth  Century 


A.D. 

Copernicus          ....      1473- 1543. 

Paracelsus  . 

•     1493-1541. 

Vesalius     . 

.     1514-1564. 

Fallopius    . 

.      1520-1563. 

Eustacliius . 

1570. 

Gesner 

.     1516-1565. 

Caesalpinus 

15 19-1603. 

Baptiste  Porta 

.     1545-1615. 

Gilbert 

.     1540-1603. 

Tycho  Brahe 

.     1546-1601. 

Galileo 

.     1 5  64- 1 642. 

Stevinus     . 

1633. 

Van  Helmont 

1 5  77-1 644. 

Giordano  Bruno 

< 

1600. 

CH.  IX.  SIXTEENTH  CENTURY.  63 


CHAPTER  IX. 

SCIENCE   OF   THE    SIXTEENTH    CENTURY. 

Rise  of  Modem  Science — Dogmatism  of  the  Middle  Ages — Reasons 
for  studying  Discoveries  in  the  order  of  their  dates — Copernican 
theory  of  the  Universe — Copernicus  goes  back  to  the  System  of 
Aristarchus — Is  afraid  to  publish  his  Work  till  quite  the  end  of  his 
life — Work  of  Vesalius  on  Anatomy — He  shows  that  Galen  made 
many  mistakes  in  describing  Man's  Structure — His  Banishment 
and  Death — The  value  of  his  Work  to  Scipnce—  Fallopius  and 
Eustachius  Anatomists — Gesner's  Works  on  Animals  and  Plants — 
He  forms  a  Zoological  Cabinet  and  makes  a  Botanical  Garden — 
His  Natural  History  of  Animals — His  classification  of  Plants  ac- 
cording to  their  Seeds — His  work  on  Mineralogy — Csesalpinus  makes 
the  First  System  of  Plants  on  Gesner's  plan — Explains  Dioecious 
Plants — Chemistry  of  Paracelsus  and  Van  Helmont, 

We  have  now  arrived  at  the  beginning  of  Modem  Science, 
when  the  foundations  were  laid  of  that  knowledge  which  we 
possess  to-day.  With  the  exception  of  some  original  disco- 
veries made  by  the  Arabs,  learned  men  during  the  Dark 
Ages  had  spent  their  time  almost  entirely  in  translating  and 
repeating  what  the  Greeks  had  taught ;  till  at  last  they  had 
come  to  believe  that  Ptolemy,  Galen,  and  Aristotle  had 
settled  most  of  the  scientific  questions,  and  that  no  one  had 
any  right  to  doubt  their  decisions.  But  as  Europe  became 
more  civilised,  and  people  had  time  to  devote  their  lives  to 
quiet  occupations,  first  one  observer  and  then  another  began 
to  see  that  many  grand  truths  were  still  undiscovered,  and 


64  SIXTEENTH  CENTURY.  pt.  hi. 

that,  though  the  Greeks  had  learned  much  about  nature,  yet 
their  greatest  men  had  only  made  the  best  theories  they 
could  from  the  facts  they  knew,  and  had  never  intended  that 
their  teaching  should  be  considered  as  complete  or  final. 

And  so  little  by  little  real  observations  and  experiments 
began  to  take  the  place  of  mere  book-learning,  and  as  soon 
as  this  happened  science  began  to  advance  rapidly — so 
rapidly  that  from  this  time  forward  we  can  only  pick  out  the 
most  remarkable  among  hundreds  of  men  who  have  added 
to  the  general  stock  of  knowledge.  A  detailed  account  of  all 
the  steps  by  which  the  different  sciences  progressed  would 
fill  many  large  volumes,  and  would  only  confuse  you,  unless 
you  aheady  knew  a  great  deal  about  the  subject.  In  this 
book  we  can  only  throw  a  rapid  glance  over  the  last  four  cen- 
turies of  modem  science,  and  try  to  understand  •  such  new 
discoveries  as  ought  to  be  familiar  to  every  educated  person. 
But  you  cannot  bear  in  mind  too  often  that  when  we  come 
to  a  great  man  who  discovers  or  lays  down  new  laws,  there 
have  always  been  a  number  of  less-known  observers  who 
have  collected  the  facts  and  ideas  from  which  he  has  formed 
his  conclusions,  although  to  mention  all  these  men  would 
only  fill  your  mind  with  a  string  of  useless  names. 

I  must  also  explain  here  why  I  have  adopted  the  plan 
of  giving  new  discoveries  in  the  order  in  which  they  oc- 
curred. You  would  no  doubt  have  understood  each  separate 
science  better  if  the  account  of  it  had  been  carried  on 
without  any  break — if,  for  example,  Astronomy  had  been 
spoken  of  first,  then  Optics,  then  Mechanics,  and  so  on. 
But  by  this  arrangement  you  would  not  see  the  gradual  way 
in  which  our  knowledge  has  grown  from  century  to  century, 
nor  how  the  work  done  in  one  science  has  often  helped  to 
bring  out  new  truths  in  another.     Therefore,  although  by 


CH.  IX.     COPERNICAN  THEORY  OF  THE  UNIVERSE.     65 

following  the  order  of  dates  we  shall  be  forced  sometimes  to 
pass  abruptly  from  one  subject  to  another,  it  will,  I  think,  be 
the  best  way  to  teach  you  the  '  History '  of  Modern  Science. 
Copernican  Theory  of  the  Universe,  1474-1543. — It  was 
stated  (p.  32)  that  about  the  year  a.d.  100  Ptolemy  formed  a 
'  System  of  the  Universe '  which  supposed  our  little  earth  to 
be  the  centre  of  all  the  heavenly  bodies  ;  and  the  sun,  toge- 
ther with  all  the  stars  and  planets,  to  move  round  us  for  our 
use  and  enjoyment.  This  system  had  been  held  and  taught 
in  all  the  schools  for  nearly  fourteen  hundred  years,  when, 
in  the  beginning  of  the  sixteenth  century,  a  man  arose  who 
set  it  aside,  and  proposed  a  better  explanation  of  the  move- 
ments which  we  see  in  the  heavens. 

In  1473,  ^  f^w  years  before  Columbus  sailed  for  America, 
•Nicolas  Copernicus,  the  son  of  a  small  country  surgeon,  was 
born  at  Thorn,  in  Poland.  From  his  earliest  boyhood  he 
had  always  a  great  love  for  science,  and  after  taking  a  doc- 
tor's degree  at  Cracow,  he  went  as  Professor  of  Mathematics 
to  Rome.  About  the  year  1500  he  returned  to  his  owm 
country  and  was  made  a  canon  of  Frauenberg,  in  Prussia. 
Here  he  set  himself  to  study  the  heavens  from  the  window 
of  his  garret,  and  often  all  night  long  from  the  steeple  of 
the  cathedral.  At  the  same  time  he  read  carefully  the  ex- 
planations which  Ptolemy  and  other  astronomers  had  given 
of  the  movements  of  the  sun  and  planets.  But  none  of 
their  theories  satisfied  him,  for  he  could  not  make  them 
agree  with  what  he  himself  observed  j  until  at  last,  after 
twenty  years  of  labour,  he  came  to  the  conclusion  that 
the  real  explanation  was  the  one  which  Aristarchus  had 
given  (p.  20),  and  which  was  called  the  Pythagorean  System, 
namely,  that  the  sun  stands  still  in  the  centre  of  our  sys- 
tem, and  that  the  earth  and  other  planets  revolve  round  it. 


66  SIXTEENTH  CENTURY.  pt.  iii. 


He  now  made  a  large  quadrant,  that  is,  an  instrument 
for  measuring  the  angular  height  of  the  sun  and  stars, 
and  with  this  he  made  an  immense  number  of  obser- 
vations on  the  different  positions  of  the  sun  during  the 
year,  all  proving  how  naturally  the  movements  of  the  dif- 
ferent planets  are  explained  by  supposing  the  sun  to  stand 
still  in  the  middle.  This  he  wrote  down  in  his  great 
work  called  'The  Revolutions  of  the  Heavenly  Bodies,' 
in  which  he  taught  that  the  earth  must  be  round,  and 
must  make  a  journey  every  year  round  the  sun.  He  gave 
his  reasons  why  Ptolemy  was  mistaken  in  believing  the 
earth  to  be  the  centre  of  the  universe,  and  added  a  dia- 
gram of  the  orbits  of  our  earth  and  of  the  planets  round 
the  sun.  He  then  went  on  to  found  upon  this  a  whole 
system  of  Astronomy,  too  complicated  for  us  to  follow 
here ;  but  he  did  not  publish  it,  because  he  was  afraid  of 
public  opinion  j  for  people  did  not  like  to  believe  that  our 
world  is  not  the  centre  of  the  whole  universe.  At  last  his 
friends  persuaded  him  to  let  his  book  be  printed,  and  a 
perfect  copy  reached  him  only  a  few  days  before  his  death, 
which  occurred  in  1543,  when  he  was  seventy  years  of  age. 

This  work  was  the  foundation  of  modern  astronomy,  and 
the  theory  that  the  earth  and  the  planets  move  round  the 
sun  has  ever  since  been  called  the  Copef^m'can  TJuory  ;  but 
at  the  time  it  was  published  very  few  persons  believed  in  it, 
and  it  was  not  till  more  than  sixty  years  after  the  death 
of  Copernicus  that  Galileo's  discoveries  brought  it  into 
general  notice. 

Work  of  Vesalius  on  Anatomy,  1542. — While  Coper- 
nicus was  proving  to  himself  that  Ptolemy's  theory  of  the 
heavens  was  not  a  true  one,  a  Belgian,  named  Vesalius,  was 
beginning  to  suspect  that  Galen,  though  a  good  physician, 


CH,  IX.  VES ALIUS  AND   GALEN.  67 

had  described  the  structure  of  man's  body  very  imperfectly, 
because  he  had  only  been  allowed  to  dissect  animals. 

Andreas  Vesalius  was  born  at  Brussels  in  15 14.  When 
he  was  quite  a  boy  he  had  a  passionate  love  for  anatomy, 
and,  as  he  had  some  little  fortune,  he  gave  up  all  his  time  to 
this  study,  and  often  ran  great  risks  in  order  to  get  bodies  to 
dissect ;  for  in  those  days  it  was  still  considered  wicked  to 
cut  up  dead  bodies.  In  the  year  1540  he  became  Professor 
of  Anatomy  at  the  University  of  Padua,  in  Northern  Italy, 
and  two  years  afterwards,  when  he  was  only  twenty- eight 
years  of  age,  he  published  his  '  Great  Anatomy,'  in  which 
Human  Anatomy.,  or  the  structure  of  man's  body,  was  care- 
fully studied  and  described ;  the  different  parts  being  illus- 
trated by  the  most  beautiful  and  accurate  wood  engravings, 
drawn  by  the  best  Italian  artists. 

In  this  book  Vesalius  pointed  out  that  Galen,  having 
learnt  his  anatomy  from  the  bodies  of  animals,  had  described 
incorrectly  almost  all  the  bones  which  are  peculiar  to  man. 
For  example,  in  animals  the  middle  part  of  the  upper  jaw, 
which  holds  the  front  and  eye-teeth,  is  a  separate  bone  from 
the  sides  of  the  jaw,  and  even  in  monkeys  it  remains  sepa- 
rate while  they  are  young  ;  but  man  is  bom  with  the  upper 
jaw  all  joined  into  one  solid  piece.  Now  Galen  had  de- 
scribed man's  upper  jaw  as  composed  of  separate  bones,  and 
therefore  it  was  clear  that  he  had  made  his  description  from 
the  skull  of  an  animal.  In  all  instances  like  this,  and  there 
are  many,  in  which  man  differs  from  animals,  Vesalius 
showed  that  it  was  necessary  to  examine  the  human  skele- 
ton, and  not  to  trust  merely  to  Galen's  teaching. 

This  was  a  great  step  in  science,  and  yet  people  had 
become  so  accustomed  to  follow  authority  blindly  that 
Vesalius    made  many   enemies  by  venturing  to  think  that 


6S  SIXTEENTH  CENTURY.  pt.  hi. 


Galen  could  be  wrong.  It  happened,  unfortunately,  'that 
one  day  when  he  was  dissecting  the  body  of  a  Spanish 
gentleman  who  had  just  died,  the  bystanders  thought  that 
they  saw  the  heart  throb.  His  enemies  seized  upon  this 
circumstance  and  accused  him  of  dissecting  a  living  man, 
and  the  judges  of  the  Inquisition  would  have  condemned 
him  to  death,  if  Charles  V.  of  Spain,  whose  physician  he 
had  become,  had  not  persuaded  them  instead  to  send  him 
on  a  pilgrimage  to  Jerusalem.  On  his  return  from  this  pil- 
grimage he  was  shipwrecked  on  the  island  of  Zante,  in  the 
Grecian  Archipelago,  and  died  of  hunger  when  he  was  only 
fifty  years  of  age.  There  are  of  course  many  faulty  descrip- 
tions in  Vesalius's  work,  for  the  study  of  anatomy  was  at 
that  time  only  beginning ;  but  he  made  the  first  attempt  to 
appeal  io  facts  instead  of  merely  repeating  what  others  had 
taught,  and  by  this  he  earned  the  right  to  be  called  the 
Founder  of  Modern  Anatomy. 

There  lived  at  the  same  time  as  Vesalius  two  other  very 
celebrated  anatomists,  Gabriel  Fallopius,  of  Modena,  and 
Barthelemy  Eustachius,  of  San  Severino,  near  Naples,  who 
both  did  a  great  deal  to  advance  anatomy.  Eustachius 
described  the  tube  running  between  the  mouth  and  the  ear 
which  is  still  called  the  Eitstachimi  tube,  and  made  many 
very  useful  experiments ;  but,  on  the  other  hand,  he  at- 
tacked Vesalius  very  bitterly  for  his  criticisms  of  Galen's 
anatomy. 

Gesner's  Works  on  Animals  and  Plants,  1551-1565. 
— We  now  come  to  one  of  the  most  interesting  lives 
of  the  sixteenth  century.  Many  of  us  know  very  little  of 
astronomy  or  anatomy,  but  any  child  who  has  gathered 
flowers  in  the  country  or  looked  at  wild  animals  in  the 
Zoolorical  Gardens  must  feel  interested  in  Gesner,  the  first 


CH.  IX.         THE  FIRST  ZOOLOGICAL    CABINET.  69 

man  since  the  time  of  Aristotle  who  wrote  anything  ori- 
ginal about  animals  and  plants. 

Conrad  Gesner  was  born  at  Zurich  in  15 16.  He  was 
the  son  of  very  poor  parents,  and,  being  left  an  orphan, 
was  educated  chiefly  by  the  charity  of  an  uncle  and  other 
friends  ;  but  his  love  of  knowledge  was  so  great  that  he 
conquered  all  difficulties,  and  after  taking  his  degree  as  a 
medical  man  in  1540,  earned  enough  by  his  profession, 
and  as  Professor  of  Natural  History  at  Zurich,  to  carry 
on  his  favourite  studies.  He  learnt  Greek,  Latin,  French, 
Italian,  English,  and  even  some  of  the  Eastern  languages, 
and  read  works  of  science  in  all  these  tongues  ;  and,  although 
he  was  very  delicate,  he  travelled  all  over  the  Alps,  Swit- 
zerland, Northern  Italy,  and  France,  in  search  of  plants, 
and  made  journeys  to  the  Adriatic  and  the  Rhine  in  order 
to  study  marine  and  fresh-water  fish.  He  employed  a  man 
exclusively  to  draw  figures  of  animals  and  plants,  and  he 
made  a  zoological  cabinet,  which  contained  the  dried  parts 
of  animals  arranged  in  their  proper  order.  This  was  pro- 
bably the  first  zoological  cabinet  which  ever  existed.  He 
also  founded  a  botanical  garden  at  Zurich,  and  paid  the 
expenses  of  it  himself.  He  took  great  interest  in  study- 
ing the  medical  uses  of  plants,  and  often  hurt  his  health 
by  trying  the  effects  of  different  herbs.  His  friends  once 
thought  that  he  had  killed  himself  by  taking  a  dose  of  a 
poisonous  plant  called  '  Doronicum,'  or  '  Leopard's  Bane,' 
but  he  recovered  and  gave  them  a  most  interesting  account 
of  his  own  symptoms. 

Between  the  years  155 1  and  1565,  Gesner  published  his 
famous  '  History  of  Animals,'  in  five  parts  ;  two  on  quadru- 
peds, one  on  birds,  one  on  fish,  and  one  on  serpents.  In  this 
book  he  describes  every  animal  then  known,  and  gives  the 


70  SIXTEENTH  CENTURY.  pt.  hi. 

countries  it  inhabits  and  the  names  it  has  been  called,  both 
in  ancient  and  modem  languages.  He  calculates  the  ave- 
rage length  of  its  life  j  its  growth,  the  number  of  young  ones 
it  will  bring  up,  and  the  illnesses  to  which  it  is  subject;  its 
instincts,  its  habits,  and  its  use ;  and  to  all  this  he  adds  care- 
ful drawings  of  the  animal  and  its  structure.  Part  of  his  in- 
formation he  gathered  from  books  and  friends,  but  a  great 
part  he  collected  himself  with  great  care,  and  to  him  we 
owe  the  first  beginning  of  the  Natural  History  of  Animals 
in  modern  times. 

In  Botany  he  made  the  first  attempt  at  a  true  classifica- 
tion of  plants,  and  pointed  out  that  the  right  way  to  disco- 
ver which  plants  most  resemble  each  other  is  to  study  their 
fiowers  and  seeds.  Before  his  time  plants  had  been  arranged 
merely  according  to  their  general  appearance ;  but  he  showed 
that  this  system  is  very  false,  and  that,  however  different 
plants  may  look,  yet,  if  their  seeds  or  flowers  are  formed 
alike,  they  should  be  classed  in  the  same  group.  He  did 
not  live  to  publish  his  great  work  on  plants,  but  left  draw- 
ings of  1,500  species,  which  were  brought  out  after  his  death. 

Gesner  also  wrote  a  book  on  Mineralogy,  in  which  he 
traced  out  the  forms  of  the  crystals  of  different  minerals  and 
drew  many  figures  of  fossil  shells  found  in  the  crust  of  the 
earth.  The  same  year  that  this  book  was  pubHshed  he  died 
of  the  plague.  When  he  knew  that  his  death  was  certain,  he 
begged  to  be  carried  into  his  museum,  which  he  had  loved 
so  well,  and  died  there  in  the  arms  of  his  wife. 

There  is  something  very  grand  and  loveable  in  the  life 
of  Gesner.  Bom  a  poor  boy,  he  struggled  manfully  upwards 
to  knowledge,  and  became  rich  only  to  work  for  science. 
Everyone  loved  him,  and  he  was  well  known  as  a  peace- 
maker among  his  literary  and  scientific  friends,  and  for  the 


CH.  IX.     THE  FIRST  CLASSIFICATION  OF  PLANTS.       71 

readiness  with  which  he  would  lay  aside  his  own  work  to 
help  others.  Yet,  though  he  had  to  earn  his  own  living  and 
died  before  he  was  forty-nine,  he  became  the  first  botanist 
and  zoologist  of  his  time,  and  left  remarkably  large  and 
valuable  works  behind  him.  He  was  one  of  the  bright 
examples  of  what  may  be  done  by  a  true  desire  for  know- 
ledge, and  a  humble,  honest,  loving  nature  j  for  while  he 
helped  others,  he  could  never  have  done  what  he  did  in 
zoology  and  botany  if  he  had  not  made  friends  all  over  the 
world,  who  were  ready  to  send  him  information  whenever 
and  wherever  they  were  able. 

First  Classification  of  Plants  by  Csesalpinus,  1583. — 
Nearly  thirty  years  after  Gesner's  death,  Dr.  Andrew  Csesal- 
pinus,  a  physician  and  Professor  of  Botany  at  Padua,  first 
tried  to  carry  out  his  system  of  grouping  plants  according  to 
their  seeds.  He  began  by  dividing  plants  into  trees  and 
herbs,  as  Theophrastus  had  done  (see  p.  17).  Then  he  di- 
vided the  trees  into  two  classes — ist,  those  which  have  the 
germ  at  the  end  of  the  seed  farthest  from  the  stalk,  as  in  the 
walnut,  where  you  will,  find  a  little  thing  shaped  like  a  tiny 
heart  lying  just  at  the  pointed  end  ;  2nd,  those  which  have 
the  germ  at  the  end  of  the  seed  which  is  nearest  the  stalk,  as 
in  the  apple.  The  herbs  he  divided  into  thirteen  classes,  ac- 
cording to  the  number  of  their  seeds  and  the  way  in  which 
they  are  arranged  in  the  seed-vessels.  Some  plants,  for 
example,  have  a  single  pod  or  seed-vessel,  with  a  number  of 
seeds  inside  it,  as  our  common  pea  j  others,  like  the  poppy, 
have  a  seed-vessel  divided  into  a  number  of  little  cells,  each 
filled  with  seeds. 

By  grouping  together  all  the  plants  which  had  the  same 
kind  of  seed-vessel,  Csesalpinus  made  thirteen  classes,  and 
formed  a  system  of  plants  which  would  have  been  a  great 


72  SIXTEENTH  CENTURY  pt.  hi. 


help  to  botanists,  and  would  soon  have  led  them  to  make 
better  systems  if  they  had  followed  it  j  but  it  was  not  gene- 
rally adopted,  and  for  nearly  a  hundred  years  longer  many 
went  on  in  the  old  way,  collecting  and  naming  plants  with- 
out trying  to  classify  them.  Caesalpmus  knew  about  1,500 
species  of  plants,  700  of  which  he  had  collected  himself.  He 
was  the  first  to  point  out  that  the  use  of  flowers  which  have 
no  seed-vessels  but  only  stajnens  (or  little  thread-like  stalks, 
tipped  with  yellow  powder),  is  to  drop  the  powder  or  pollen 
on  flowers  which  have  only  seed-vessels  and  no  stamens, 
and  by  this  means  to  cause  the  seeds  to  grow  and  ripen. 
Such  plants  which  have  the  stamens  in  one  flower  and  the 
seed-vessel  in  another  are  now  called  Dioecious  plants. 

Chemistry  of  Paracelsus  and  Van  Helmont,  1520- 
1600. — There  is  very  little  worthy  of  notice  in  the  chemistry 
of  the  sixteenth  century;  but  we  must  mention  in  passing 
two  famous  men  :  Paracelsus,  who  was  bom  1493  at  Einsiedel 
in  Switzerland,  and  Van  Helmont,  bom  at  Brussels  in  1577. 

Paracelsus  was  at  one  time  Professor  of  Physic  and  Sur- 
gery at  Basle,  but  he  gave  up  his  professorship  and  travelled 
about  Europe  during  the  greater  part  of  his  life.  Among 
other  things,  he  pointed  out  that  air  feeds  flame,  and  that,  if 
you  put  iron  into  sulphuric  acid  and  water,  a  peculiar  kind  of 
air  rises  from  it.  He  also  succeeded  in  separating  gold  out 
of  a  mixture  of  gold  and  silver  by  using  aquafortis  or  nitric 
acid,  which  dissolves  the  silver  and  lets  the  gold  fall  to  the 
bottom  of  the  vessel.  He  did  not,  however,  make  many 
discoveries  which  are  valuable  now,  and  he  taught  a  great 
deal  that  was  absurd  and  bombastic. 

Van  Helmont  was  also  a  wandering  physician,  but  as  a 
chemist  he  was  more  careful  in  his  experiments  than  Paracel- 
sus.   He  seems  to  have  known  a  great  many  different  gases, 


CH.  IX.         PARACELSUS  AND    VAN  HELMONT.  73 

though  he  did  not  describe  them  clearly,  and  he  particularly 
mentions  the  gas  which  rises  from  beer  and  other  liquids 
which  ferment.  He  called  this  Gas  sylvestre.  The  chief 
thing  to  remember  about  Van  Helmont  is  that  he  was  the 
first  writer  to  use  the  word  '  gas/  which  he  took  from  the 
German  word  'geist/  meaning  'spirit' 


Chief  Works  consulted, — Rees's  'Encyclopaedia,'  art.  'Coperni- 
cus ; '  *  Encyclopaedia  Metropolitana, '  art.  '  Astronomy  ; '  '  Biographie 
Universelle,'  art.  'Copernicus;'  Gassendi's  'Life  of  Copernicus ; ' 
'Encyclopaedia,'"  art.  'Anatomy;'  Cuvier,  'Histoire  des  Sciences 
Naturelles,'  1845;  D'Orbigny,  'Diet,  des  Sciences  Naturelles' — In- 
troduction ;  '  Encyclopaedia, '  art.  '  Botany  ; '  Hoefer,  '  Histoire  de  la 
Physique  et  de  la  Chimie,'  1850. 


74  SIXTEENTH  CENTURY,  pt.  hi. 


CHAPTER  X. 

SCIENCE    OF   THE    SIXTEENTH    CENTURY   (CONTINUED). 

Baptiste  Porta  discovers  the  Camera  Obscura — Shows  that  our  Eye  is 
like  a  Camera  Obscura — Makes  a  kind  of  Magic  Lantern  by  Sun- 
light —  Kircher  afterwards  makes  a  Magic  Lantern  by  Lamplight 
— Dr.  Gilbert's  discoveries  in  Electricity — Tycho  Brahe,  the  Danish 
Astronomer — Builds  an  Observatory  on  the  Island  of  Huen — Makes 
a  great  number  of  Observations,  and  draws  up  the  Rudolphine 
Tables — Galileo  discovers  the  principle  of  the  Pendulum — Cal- 
culates the  velocity  of  Falling  Bodies,  and  shows  why  it  in- 
creases— Shows  that  Unequal  Weights  fall  to  the  Ground  in  the 
same  time — Establishes  the  relations  of  Force  and  Weight — Sum- 
mary of  the  Science  of  the  sixteenth  century. 

Baptiste  Porta's  discoveries  about  Light,  1560. — The  next 
discovery  in  science  was  about  Light,  and  it  was  made  by  a 
boy  only  fifteen  years  of  age.  Baptiste  Porta  was  born  in 
Naples  ia  1545.  He  was  so  eager  for  new  knowledge  that 
when  quite  a  boy  he  held  meetings  in  his  house  for  any  of 
his  friends  to  read  papers  about  new  experiments.  These 
meetings  were  called  *  the  Academy  of  Secrets,'  and  in  the 
year  1560,  when  Porta  was  fifteen,  he  published  an  account  of 
them  in  a  book  called  *  Magia  Naturalist  or  '  Natural  Magic' 
In  the  seventeenth  chapter  of  this  book  he  relates  the  fol- 
lowing experiment  which  he  had  made  himself 

He  says  he  found  that  by  going  into  a  darkened  room 
when  the  sun  was  shining  brightly,  and  making  a  very  small 
hole  in  the  window-shutter,  he  could  produce  on  the  wall  of 


CH.   X. 


CAMERA  OBSCURA '  AND  AIA  GIC  LANTERN.     75 


the  room,  opposite  the  hole,  images  of  things  outside  the 
window.  These  images  were  exactly  the  shape  of  the  real 
objects,  and  had  always  their  proper  colours  ;  as  for  example, 
if  a  man  was  standing  against  a  tree  outside  the  house,  the 
green  leaves  of  the  tree  and  the  different  colours  of  the  man's 
clothes  would  be  clearly  shown  on  the  wall.  There  was 
only  one  peculiarity  about  the  picture,  it  was  always  upside 
down,  so  that  the  man  stood  on  his  head,  or  the  tree  \\A\\\ 
its  trunk  in  the  air.     The  smaller  the  hole  was,  the  clearer 

Fig.  7. 


were  the  outline  and  the  colours  of  the  image,  and  Porta 
found  that  by  putting  a  convex  lens  (that  is,  a  glass  with  its 
surfaces  bulging  in  the  centre,  see  p.  49)  into  the  hole  he 
could  get  a  still  brighter  and  clearer  picture  at  a  particular 
point  in  the  room. 

Porta  knew  from  the  works  of  Alhazen  that  rays  of 
light  are  reflected  in  all  directions  from  every  object,  and  he 
explained  this  image  on  the  wall  quite  correctly,  by  saying 
that  the  small  hole  lets  in  only  one  ray  from  each  point  of  an 
object  outside  j  the  other  rays  and  those  from  the  sky  and 
other  objects  being  kept  out  by  the  shutter.  Thus  these 
single  rays  .fall  directly  on  the  wall  without  being  mingled 
with  others,  and  so  make  a  clear  picture.  It  is  easy  to  see 
from  fig.  7  that  the  image  must  be  upside  down,  because  the 
rays  cross  in  going  through  the  hole.  This  simple  discovery 
of  Porta's  is  called  the  '  Camera  Obscura,  or  *  Dark  Chamber.' 


76  SIXTEENTH  CENTURY.  pt.  hi. 

You  may  perhaps  have  been  into  one  at  the  sea-side,  where 
they  build  them  for  visitors  to  watch  the  coloured  reflec- 
tion of  the  passers-by.  In  the  camera  obscura,  as  it  is  now 
made,  the  glasses  are  so  arranged  that  the  figures  are  up- 
right. 

Porta  saw  at  once  how  useful  this"  invention  would  be  for 
making  accurate  drawings  of  objects ;  for,  by  tracing  out  with 
colours  on  the  wall  the  figure  of  the  man  or  tree  as  it  stood, 
he  could  get  a  small  image  of  it  with  all  its  proportions  and 
colours  correct.  But,  what  is  still  more  important,  he  was 
led  by  this  experiment  to  understand  how  we  see  objects, 
and  to  prove  that  Alhazen  was  right  in  saying  that  rays 
of  light  from  the  things  around  us  strike  upon  our.  eye. 
For,  said  Porta,  the  little  hole  in  the  shutter  with  the  lens 
in  it,  is  like  the  little  hole  in  our  eye,  which  also  con- 
tains a  natural  convex  lens ;  and  we  see  objects  clearly 
because  the  rays  pass  through  this  small  hole.  He  did 
not,  however,  know  which  part  of  our  eye  represents  the 
wall  on  which  the  figure  is  thrown,  nor  why  we  see  objects 
upright ;  we  shall  see  (p. 96)  that  Kepler  discovered  this  many 
years  afterwards. 

When  Porta  had  succeeded  in  getting  clear  images  of 
real  things  on  the  wall,  he  began  to  try  painting  artificial 
pictures  on  thin  transparent  paper  and  passing  them  across 
the  hole  in  the  shutter,  and  he  found  that  the  sun  threw  a 
very  fair  picture  of  them  on  the  wall.  In  this  way  he  pro- 
duced representations  of  battles  and  hunts,  and  so  made  a 
step  towards  the  Magic  Lantern.  He  seems,  however,  never  to 
have  tried  it  by  lamplight ;  this  was  done  by  Kircher,  a  Ger- 
man, about  fifty  years  later.  There  is  no  doubt  that  Porta  had 
a  ver}^  good  notion  of  how  to  use  two  magnifying  glasses  so  as 


CH.  X.  DISCOVERY  OF  ELECTRICITY.  77 

to  make  objects  appear  nearer  and  larger,  but  it  is  not  certain 
that  he  ever  really  made  a  telescope. 

Dr.  Gilbert,  the  Founder  of  the  Science  of  Electricity, 
1540-1603. — It  was  about  this  time,  while  Baptiste  Porta 
was  making  experiments  on  light  in  Italy,  that  an  English- 
man named  Gilbert  made  the  first  step  in  one  of  the  most 
wonderful  and  interesting  of  all  the  sciences,  namely,  that  of 
Electricity.  So  long  ago  as  the  time  of  the  Greeks  it  was 
already  known  that  amber,  when  rubbed,  will  attract  or  draw 
towards  it  bits  of  straw  and  other  light  bodies,  and  it  is  from 
the  Greek  word  electron — amber,  that  our  word  electricity  is 
taken. 

Until  the  sixteenth  century,  however,  no  one  had  made 
any  careful  experiments  upon  this  curious  fact,  and  it  was 
Dr.  Gilbert,  a  physician  of  Colchester,  who  first  discovered 
that  other  bodies  besides  amber  will,  when  rubbed,  attract 
straws,  thin  shavings  of  metals,  and  other  substances.  You 
can  easily  try  this  for  yourself  by  rubbing  the  end  of  a  stick 
of  common  sealing-wax  on  a  piece  of  dry  flannel,  and  then 
holding  the  rubbed  end  near  to  some  small  pieces  of  light 
paper,  or  some  feathers  or  bran.  You  will  find  that  these 
substances  will  spring  towards  the  sealing-wax  and  cling  to 
it  for  short  time,  being  held  there  by  the  electricity  which 
has  been  produced  by  rubbing  the  sealing-wax. 

Gilbert  showed  that  amber,  jet,  diamond,  crystal,  sul- 
phur, sealing-wax,  alum,  and  many  other  substances,  have 
this  power  of  attraction  when  they  are  rubbed,  and  he  also 
proved  that  the  attraction  was  stronger  when  the  air  is  dry 
and  cold  than  when  it  is  warm  and  moist.  This  may  seem 
very  little  to  have  discovered  compared  to  the  wonderful 
facts  which  we  now  know  about  electricity  ;  but  it  was  the 
first  step,  and  Gilbert's  book  on  *  Magnetism '  (as  he  called 


78  SIXTEENTH  CENTURY.  pt.  hi. 

it),  which  was  published  in  1600,  must  be  remembered  as 
the  earUest  beginning  of  the  stuSy  of  electricity. 

Tycho  Brahe,  Astronomer,  1546-1601. — We  must  now 
return  to  Astronomy,  in  which  during  the  next  eighty  years 
wonderful  discoveries  were  made  by  three  celebrated  men, 
Tycho  Brahe  the  Dane,  Galileo  the  Italian,  and  Kepler  the 
German. 

Tycho  Brahe  was  born  in  the  year  1546,  at  Helsinborg, 
a  town  in  Sweden,  which  at  that  time  belonged  to  the  Danes. 
When  he  was  only  fourteen  he  was  so  much  astonished  that 
the  astronomers  had  been  able  to  foretell  exactly  the 
moment  when  an  eclipse  of  the  sun  took  place  in  1560, 
that  he  determined  to  learn  this  wonderful  science,  which 
could  predict  events.  His  father  had  intended  him  to  be  a 
lawyer,  but  Tycho  bought  a  globe  and  books  with  his  own 
money,  and  studied  astronomy  in  secret ;  till  at  last  his 
family  consented  to  let  him  follow  his  Q-^mi  inclination,  and 
from  that  time  he  gave  himself  up  to  that  science,  planning 
and  making  the  most  beautiful  instruments  for  taking  obser- 
vations in  the  heavens. 

At  this  time  the  theory  of  Copernicus  had  made  very 
little  impression,  and  Tycho  Brahe  rejected  it  altogether 
and  made  a  theory  of  his  own  called  the  Tychonic  system, 
which  was,  however,  soon  laid  aside  and  forgotten.  This, 
however,  mattered  very  little,  for  the  useful  work  which 
Tycho  did  was  not  to  lay  down  new  laws,  but  to  collect  an 
immense  number  of  accurate  facts  which  were  invaluable  to 
the  astronomers  who  came  after  him.  For  twenty-five  years 
he  lived  in  the  little  island  of  Huen,  in  the  Baltic,  which 
the  King,  Frederick  II.  of  Denmark,  had  given  him, 
making  accurate  observations  of  the  different  movements  of 
the  planets,  and  determining  the  positions  of  the  fixed  stars, 


CH.  X.  ORIGIN  OF  THE  FEADULUM.  79 


of  which  he  catalogued  777.  He  built  there  a  magnificent 
observatory,  which  he  called  Uranienburg,  or  the  City  of  the 
Heavens,  and  filled  it  with  instruments  of  every  kind,  which 
enabled  him  to  keep  a  register  of  the  different  positions  of 
the  heavenly,  bodies  night  after  night. 

When  Frederick  II.  died,  Tycho  was  persecuted  and 
driven  into  exile  by  some  envious  people  who  grudged  him 
the  pension  he  was  receiving.  He  then  went  to  Bohemia, 
under  the  protection  of  the  Emperor  Rudolph  II.,  and  here 
he  drew  up  the  valuable  astronomical  tables  called  the 
Rudolphine  tables,  which,  as  we  shall  afterwards  see,  were  of 
immense  use  to  Kepler.  Tycho  died  ini6oi,  before*  Galileo 
and  Kepler  made  their  greatest  discoveries. 

Galileo's  discovery  of  the  principle  of  the  Pendulum, 
and  of  the  rate  of  Falling  Bodies,  1564-1600.— Galileo  dei 
Galilei  was  born  at  Pisa  in  1564.  His  father,  though  of 
good  family,  was  poor,  but  being  himself  a  man  of  talent 
and  education,  he  made  great  exertions  to  send  his  son  to 
the  University  of  Pisa,  meaning  to  educate  him  as  a  doctor. 
Here  Galileo  studied  medicine  under  the  famous  botanist 
Caesalpinus ;  but  having  also  begun  to  learn  geometry,  he 
became  so  wrapt  up  in  this  pursuit  that  his  father  found  it 
was  useless  to  check  him,  and  therefore  wisely  let  him  follow 
his  natural  bent.  It  was  while  he  was  still  at  the  University, 
and  before  he  was  twenty  years  of  age,  that  Galileo  made  his 
first  discovery.  When  watching  a  lamp  one  day  which  was 
swinging  from  the  roof  of  the  cathedral,  he  noticed  that, 
whether  it  made  a  long  or  a  short  swing,  it  always  took  the 
same  time  to  go  from  one  side  to  another.  To  tnake  quite 
sure  of  this  he  put  his  finger  on  his  own  pulse,  and,  compar- 
ing its  throbs  with  each  swing  of  the  lamp,  found  that  there 
was  always  the  same  number  of  beats  to  every  swing.     Fol- 


8o  SIXTEENTH  CENTURY.  pt.  hi. 


lowing  up  this  simple  observation  he  discovered  that  a  weight 
at  the  end  of  a  cord  will  always  take  the  same  time  to  swing 
backwards  and  forwards  so  long  as  the  cord  is  of  the  same 
length  and  the  arc  through  which  the  weight  moves  is  small. 
This  was  the  beginning  of  pendulums,  such  as  we  now  have 
to  our  clocks,  but  at  first  they  were  only  used  by  physicians 
to  count  the  rate  at  which  a  patient's  pulse  beats. 

In  1589  Ferdinand  de'  Medici,  Duke  of  Tuscany,  having 
heard  of  Galileo's  talents,  made  him  Lecturer  of  Mathematics 
at  Pisa,  and  it  was  while  he  held  this  post  that  he  made  his 
next  discovery,  which  was  about  falling  bodies.  He  observed 
that  a  stone  or  any  other  body,  dropped  from  a  height,  falls 
more  and  more  quickly  from  the  time  it  starts  till  it  reaches 
the  ground,  and  after  many  experiments  he  succeeded  in 
calculating  at  what  rate  its  falling  increases.  At  the  end  of 
the  first  second  it  will  be  falling  at  the  rate  of  32  feet  per 
second,  at  the  end  of  two  seconds  it  will  be  falling  at  the 
rate  of  64  feet  per  second,  at  the  end  of  three  seconds  at  the 
rate  of  96  feet  per  second,  and  so  it  will  continue,  falling  32 
feet  faster  every  second  till  it  reaches  the  ground. 

Galileo  explained  this  increase  of  velocity,  or  quickness 
of  falling,  in  the  following  way  :  It  is  the  weight  of  the  stone, 
he  said,  which  drags  it  down  ;  and  when  it  had  been  once 
started  downwards  by  its  weight,  it  would  go  on  moving  at 
the  same  rate  for  ever,  without  any  more  dragging.  But  the 
weight  still  goes  on  pulling  it  down  just  as  much  at  the  end 
of  the  first  second  as  it  did  when  it  started,  and  so  the  stone 
falls,  first  with  the  drag  of  its  start,  then  with  the  drag  of  the 
first  secon<i  added,  then  of  the  next,  and  the  next  all  added 
together,  until  it  reaches  the  ground. 

This  was  quite  a  true  explanation,  so  far  as  it  went,  and 
Galileo  went  on  to  prove  another  fact,  which  sounds  very 


en.  X.-  THE  RATE    OF  FALLING  BODIES.  8i 

strange  at  first,  namely,  that  if  you  let  two  weights,  one 
light  and  the  other  heavy,  drop  from  the  same  height,  they 
will  both  take  exactly  the  same  time  in  falling  to  the  ground. 
Galileo  could  not  make  the  learned  men  of  Pisa  believe 
this,  because  Aristotle  had  said  that  a  ten-pound  weight 
would  fall  ten  times  as  fast  as  a  one-pound  weight ;  so  to 
convince  them  he  carried  different  weights  up  to  the  top  of 
the  Tower  of  Pisa,  and  let  them  fall  before  their  eyes. 
Still,  though  they  saw  them  reach  the  ground  at  the  same 
moment,  they  would  not  believe,  so  obstinately  were  they  de- 
termined to  think  with  Aristotle ;  and  they  actually  annoyed 
Galileo  so  much  on  account  of  his  opinions  that  he  left  Pisa 
and  became  a  professor  at  Padua  in  1592. 

The  best  way  for  you  to  convince  yourself  that  Galileo 
was  right  and  they  were  wrong  will  be  to  take  some  large 
soft  clay  balls,  say  five,  each  exactly  the  same  weight,  and 
let  them  drop  at  the  same  moment  from  the  same  height — 
you  can  see  at  once  that  they  will  all  reach  the  ground 
together.  Then  press  four  of  the  balls  one  against  the 
other  so  that  they  stick  together.  They  will  now  be  four 
times  heavier  than  the  remaining  ball,  and  yet  if  you  let 
them  drop  from  the  same  height  again,  there  is  no  reason 
why  the  four  should  fall  any  faster  merely  because  they  are 
stuck  together  than  when  they  were  separate,  and  so  the  five 
will  reach  the  ground  together  as  they  did  before.  I  have 
said  take  large  balls,  because  if  they  are  not  tolerably  heavy 
the  air  will  interfere  with  their  falling  accurately ;  indeed,  to 
make  the  experiment  very  truly  it  ought  to  be  made  in  a 
vacuum,  that  is,  a  space  from  which  the  air  has  been  pumped 
out,  for  it  is  easy  to  see  that  air,  like  water,  will  buoy  up  a 
light  body  more  than  a  heavy  one,  and  so  would  cause  it  to 
be  longer  in  falling.     But  air-pumps  were  not  invented  in 


82  SIXrEENTH  CENTURY.  it.  ill. 

Galileo's  time,  so  he  could  not  make  the  experiment  very 
accurately. 

In  the  year  1592  Galileo  established  another  law  in 
mechanics  which  is  of  great  value,  namely,  that  any  force 
which  will  lift  a  weight  of  two  pounds  up  one  foot'  will  lift  a 
weight  of  one  pound  up  two  feet,  or  in  other  words,  just  as 
much  as  you  make  a  weight  lighter,  so  much  higher  the 
same  force  can  lift  it.  If  you  double  the  weight,  the  same 
force  will  only  lift  it  half  as  high  ;  if  you  treble  the  weight,  it 
will  only  lift  it  one-third  as  high,  and  so  on.  This  law  is  of 
immense  value  in  determining  the  balance  of  machines,  but 
we  cannot  examine  it  further  here.  At  about  the  same  time 
that  Galileo  was  discovering  these  laws  of  motion,  a  famous 
engineer,  named  Stevinus,  of  Bruges,  published  a  little  book, 
in  which  he  made  known  some  very  important  laws  about 
the  rest  and  motion  of  bodies,  which  formed  the  foundation 
of  the  modem  science  of  statics,  or  the  study  of  bodies  at 
rest. 

Summary  of  the  Science  of  the  Sixteenth  Century. — 
And  now  we  must  pause  for  a  moment  in  the  history  of 
Galileo,  for  his  astronomical  discoveries  belong  to  the  next 
century,  and  before  entering  upon  them  we  must  reckon 
up  the  advances  which  had  been  made  in  science  during 
the  past  hundred  years. 

I  think  you  will  agree  with  me  that  at  least  one  grand  step 
had  been  made  when  men  learned  to  examine  for  themselves, 
and  were  no  longer  content  merely  to  repeat  like  parrots  what 
the  Greeks  had  handed  down  to  them.  Copernicus  had 
shown  in  astronomy,  Vesalius  in  anatomy,  and  Galileo  in 
mechanics,  that  it  was  no  longer  enough  to  quote  passages 
from  Ptolemy,  Galen,  and  Aristotle  j  but  men  must  take  the 
trouble  to  examine  the  works  of  nature  for  themselves,  if 


CH.  X.  CONCLUDING  REMARKS.  83 

they  wished  really  to  understand  the  laws  of  the  Great 
Creator. 

This,  in  itself,  was  a  great  advance ;  but  beyond  this 
Copernicus,  by  his  new  system,  had  opened  the  way  for 
grand  astronomical  discoveries  which  you  will  see  followed 
quickly  in  the  next  century,  and  Tycho,  by  -his  long  and 
patient  observations,  had  stored  up  facts  for  the  use  of  those 
who  came  after  him.  In  the  same  way  Vesalius  in  anatomy, 
and  Gesner  and  Csesalpinus  in  natural  history,  had  laid  a 
foundation  for  the  regular  study  of  living  beings,  and  had 
roughly  sketched  out  a  plan  of  classification.  In  the  subject 
of  light.  Porta  had  invented  the  camera  obscura,  explained 
the  principle  upon  which  it  acts,  and  in  doing  this  had  made 
important  discoveries  about  the  action  of  light  upon  our 
eye,  and  the  use  of  lenses^  or  convex  and  concave  glasses, 
in  magnifying  objects.  Lastly,  Galileo  had  discovered  the 
principle  of  the  pendulum  and  the  rate  of  falling  bodies, 
and  was  now  on  the  brink  of  the  discovery  of  the  telescope 
and  all  the  wonders  which  it  has  revealed. 

Meanwhile  the  sixteenth  century  closed  with  one  very 
sad  event,  which  must  be  mentioned  here.  Giordano  Bruno, 
a  Dominican  friar,  who  was  born  about  the  year  1550,  at  Nola, 
in  Italy,  was  one  of  the  first  people  who  openly  taught  that 
the  Copernican  system  was  true.  He  ought  to  be  peculiarly 
interesting  to  us,  because  he  was  the  first  person  to  teach  in 
England  that  the  earth  moves  round  the  sun.  But  poor 
Bruno  was  a  very  plain  outspoken  man,  and  his  bold 
language  brought  him  to  a  sad  but  noble  death.  When 
people  said  he  should  not  spread  the  Copernican  system 
because  it  was  contrary  to  the  Bible,  he  answered  boldly 
that  the  Bible  was  meant  to  teach  men  how  to  love  God 
and   live    rightly,  and   not  to  settle  questions   of  science. 


84  SIXTEENTH  CENTURY.  pt.  in. 

Most  people  now  would  say  that  Bruno  was  right,  but  the 
judges  of  the  Inquisition  did  not  think  so,  and  were  so 
alarmed  at  his  opinions  that  they  condemned  him  to  death. 
In  the  year  1600,  just  after  the  century  closed,  Bruno  was 
burnt  at  the  stake  in  Rome  as  an  atheist,  partly  because  he 
insisted  on  repeating  that  the  earth  is  not  the  centre  of  the 
universe,  and  that  there  may  be  other  inhabited  worlds  be- 
sides ours. 


Chief  Works  consulted.  — Whewell's  *  Inductive  Sciences  ; '  Brewster's 
'Optics;'  Brewster's  'Martyrs  of  Science,'  1874;  'Encyclopaedia 
Britannica,'  art.  '  Astronomy ;  '  Drinkwater's  *  Life  of  Galileo  ;  ' 
Rossiter's  *  Mechanics,'  1873 ;  Cuviei",  *  Histoire  de  Sciences  Natu- 
relles  ; '  Baden  Powell's  '  Natural  Philosophy.* 


SCIENCE    OF    THE 
SEVENTEENTH    CENTURY 


Chief  Men  of  Science  in  the  Seventeenth  Century, 


A,D. 

Galileo 15  64- 1642. 

Kepler 

. 

. 

15  71-1630. 

Gassendi     . 

1592-1655. 

Horrocks    . 

1619-1641. 

Newton 

1 642- 1 72  7. 

Halley 

1656-1742. 

Francis  Bacon     . 

1561-1626. 

Descartes    . 

1596-1650. 

Snellius 

1591-1626. 

Drebbel      . 

I 5 72-1634. 

Torricelli    . 

1 608-1 647. 

Guericke    . 

1 602-1 686. 

Boyle 

1626-1691. 

Hooke 

I 635-1 702. 

Huyghens  . 

,     1629-1695. 

Roemer 

.     1644-17 10. 

Mayow 

.     1645-1679. 

Beeclier 

.     1625-1682. 

Stahl 

.     1 660-1 734. 

Steno 

.     1638-1687. 

Scilla 

.     I 639-1 700. 

Woodward 

.     1661-1727. 

Harvey 

.     1578-1657. 

Asellius 

. .    1581-1626. 

RUdbeck    . 

.     1 630-1 702. 

Malpighi    . 

.     1628-1694. 

Leeuwenhoeck 

.     1632-17^3. 

Grew 

.     1628-1711. 

Ray   . 

.     1 628-1 705. 

Wniughby 

.     1635-1672. 

CH.  XI.  GALILEO.  87 


CHAPTER   XL 

SCIENCE    OF    THE   SEVENTEENTH    CENTURY. 

Astronomical  discoveries  of  Galileo — The  Telescope — Galileo  esamines 
the  Moon,  and  discovers  the  Earth-light  upon  it — Discovers  Jupiter's 
four  Moons — Distinguishes  the  Fixed  Stars  from  the  Planets — The 
phases  of  Venus  confirm  the  Copernican  theory — Galileo  notices 
Saturn's  Ring,  but  does  not  distinguish  it  clearly — Observes  the 
spots  on  the  Sun — The  Inquisition  force  him  to  deny  the  movement 
of  the  Earth —  Blindness  and  Death  of  Galileo. 

Astronomical  Discoveries  of  Galileo,  1609-1642. — The  seven- 
teenth century  was  not  many  years  old  when  Galileo  startled 
the  world  with  discoveries  such  as  had  never  been  heard  of 
before.  He  relates  that  when  quite  a  young  man  he  was  so 
struck  with  an  account  given  by  some  of  his  companions  of 
a  lecture  on  the  Copernican  theory,  that  he  determined  to 
study  it,  and  he  soon  became  convinced  of  its  truth.  Never- 
theless he  saw  how  difficult  it  would  be  io  prove  that  the  earth 
moves  round  the  sun,  and  not  the  sun  round  the  earth. 

When  he  went  to  Padua  he  gave  a  great  deal  of  time  to 
the  study  of  astronomy,  and  had  already  made  some 
remarkable  observations,  when  one  day,  in  the  year  1609, 
being  in  Venice,  he  heard  that  a  Dutch  spectacle-maker  had 
invented  an  instrument  which  made  distant  things  appear 
close  at  hand. 

This  discovery,  which  Bacon  and  Porta  had  foreseen, 
was  made  at  last  almost  by  accident  in  Holland,  by  two 
spectacle-makers,  Zacharias  Jansen  and  Henry  Lippershey. 


88  SEVENTEENTH  CENTURY,  ft.  hi. 

It  is  related  that  Jansen's  children  when  playing  one  day  with 
two  powerful  magnifying  glasses,  happened  to  place  them 
one  behind  the  other  in  such  a  position  that  the  weathercock 
of  a  church  opposite  the  house  seemed  to  them  nearer  and 
larger  than  usual,  and  their  father,  when  he  saw  this,  fixed 
the   glasses  on  a  board  and  gave  them  as  a  curiosity  to 
Prince  Maurice  of  Nassau.    -Whether  this  story  be  true  or 
not,  it  is  certain  that  in  the  year  1609,  both  Jansen  and 
Lippershey  made  these  rough  telescopes  as  toys,  though  they 
did  not  know  how  useful  they  might  be.     But  when  Galileo 
heard  of  it  he  saw  at  once  what  valuable  help   it   might 
afford  in  studying  the  heavens  ;  and  he  set  to  work  imme- 
diately, and  soon  succeeded  in  making  a  useful  instrument. 
A  diagram  of  Galileo's  telescope  is  given  in  Fig.  8.     It 
was  made  on  the  same  principle  as  opera-glasses  are  now, 
with  one  convex  lens  a  b,  which  makes  the  rays  from  the 
object  bend  inwards  or  converge,  and  one  concave  \^Vi.s  Q,  d, 
which  makes  them  bend  outwards  or  diverge  before  they 
come  to  a  focus.    In  Fig.  8  one  complete  cone  of  rays  is 
drawn  coming  from  the  point  in,  and  the  outline  of  another 
cone  from  the  point  n  j  there  are  really  similar  cones  coming 
from  all  points  along  the  arrow,  but  it  is  impossible  to  give 
these  in  a  diagram.     Each  set  of  rays  as  they  fall  on  the 
lens  A  B,  are  made  to  converge,  so  that  they  would  end  in  a 
point  or  focus,  if  they  were  not  caught  by  the  lens  c  d.     But 
this  lens  having  its  surfaces  curved  inwards  makes  the  rays 
bend  outwards  or  diverge  again,  so  that  the  end  of  the  cone  m 
reaches  the  eye  in  parallel  lines  at  m'  m'  and  the  cone  n  at 
n'  n'.     From  here,  as  you  will  remember  (see  p.  49),  we 
follow  them  out  in  straight  lines,  and  see  the  image  at  the 
angle  m  ^  n,  so  that  it  appears  greatly  magnified.     If  you 
look  at  any  object  through  ome  tube  of  an  opera-glass,  and 


CH.  XI. 


GALILEOS   TELESCOPE. 


89 


keep  the  other  eye  open  so  as  to  see  the  object  at  its  natural 
distance,  you  can  cover  the  real  image  with  the  magnified 
one,  and  thus  see  the  magnifying  power  of  your  glass.  But 
when  you  do  not  compare  them  in  this  way  you  do  not 
realise  how  much  the  object  is  enlarged,  because  it  appears 

Fig.  8. 


Galileo's  Telescope. 


A  B,  Convex  lens ;  C  D,  concave  lens  next  the  eye ;  ni  n,  real  arrow ;  M  N, 
apparent  size  of  arrow  ;  tn'  m'  and  n'n',  end  of  the  cones  of  rays  m  and  n  as 
they  reach  the  eye  ;  M  <?  n,  angle  at  which  the  magnified  arrow  is  seen. 

to  come  nearer,  so  as  to  be  at  some  point  between  m  n 
and  0,  and  to  be  less  magnified  in  consequence.  I  must 
warn  you  that  both  in  this  diagram  and  the  one  at  p.  97 
the  proportions  are  very  much  distorted,  because  a  star  or 
even  a  house  would  be  an  immense  distance  oif  as  compared 
with  the  length  of  a  telescope,  whereas  the  arrow  is  obliged 
to  be  drawn  here  as  near  to  the  lenses  as  they  are  to  each 
other. 

Secondary  Light  of  the  Moon. — Galileo's  first  telescope 
only  magnified  three  times,  that  is,  made  an  object  three 
times  larger ;  but  he  made  a  second  which  magnified  eight 
times,  and  then  he  turned  it  to  the  moon  and  began   to 


90  SEVENTEENTH  CENTURY.  pt.  iii. 

examine  the  surface  of  that  sateUite.    He  saw  the  mountains 
_of  the  moon^_aiidjhe_deepJi^^ 

the  wids  plains  which  he  mistook__fbi^^oceariSi__Then  he 
noticed  that  curious  light"  calTed  the  secondary  light,  which 
jtnay  be  seen  on  the  dark  side^^ofjhe^maon  arherL-on^L-one 
quarter~oriFis'^right;  and  shining.  Gahleo  discovered  that 
this"curious  figEFTs  a  reflection  from  the  earth  j  for  you  must 
know  that  we  reflect  the  sun's  Hght  back  to  the  moon  just  in 
the  same  way  as  the  moon  does  back  to  us,  and  at  the  time 
when  we  see  a  new  moon,  the  man  in  the  moon  (if  there 
were  such  a  person)  would  see  a  large  full  earth  and  could 
wander  about  at  night  by  earth-light  as  we  do  by  moonlight. 
Look  up  at  the  new  moon  just  about  dusk  in  the  evening, 
and  if  it  is  a  clear  night  you  will  most  likely  be  able  to  see 
a  faint  outline  of  the  dark  side  of  the  moon,  which  is 
caused  by  our  earth-light  shining  upon  it. 

Jupiter's  Moons. — When  Galileo  had  studied  the  moon 
and  gazed  with  intense  delight  on  the  myriads  of  tiny  stars 
in  the  Milky  Way,  he  next  turned  his  telescope  to  the  planet 
Jupiter.  To  his  great  surprise  he  saw  three  small  shining 
bodies  like  stars  close  to  Jupiter  which  were  quite  invisible  to 
the  naked  eye.  Tw^o  of  them  were  on  the  east  side  of  the 
planet  and  the  other  on  the  west.  He  waited  eagerly  for  the 
second  night,  to  see  if  Jupiter  would  move  away  from  these 
stars,  but  he  found  them  still  together,  only  the  two  stars 
which  had  been  on  the  east  side  had  now  moved  round  to 
the  west,  and  they  were  nearer  to  each  other  than  they  had 
been  before.  He  was  quite  puzzled  as  to  how  this  could 
have  happened,  and  watched  and  watched  for  many  nights 
whenever  the  clouds  would  allow  him ;  and  at  last,  on  the 
fourth  night  after  he  had  first  seen  them,  he  came  to  the 
conclusion  that  all  three  stars  were  moving  round  and  round 


CH.  XI.  ASTRONOMICAL  DISCOVERIES.  91 

Jupiter,  as  the  moon  goes  round  our  earth.  A  few  nights 
later  he  found  that  there  was  a  fourth  star  which  went  round 
with  them ;  and  so  Gahleo  discovered  Jupiter's  four  moons 
in  the  year  16 to. 

This  was  the  first  fact  in  favour  of  the  Copernican  theory 
which  ordinary  people  could  understand.  The  planets  had 
till  now  been  looked  upon  simply  as  lights  in  the  sky  moving 
round  the  earth  ;  but  now  it  could  not  be  doubted  that 
Jupiter  at  least  was  something  more  than  this,  for  he  had  a 
system  like  our  own,  with  four  moons,  to  give  him  light  by 
night,  instead  of  one.  As  usual  there  were  a  great  number 
of  people  who  were  alarmed  at  the  fact  that  our  little  earth 
should  not  be  the  central  body  in  the  heavens,  and  many 
astronomers  would  not  believe  that  Galileo  had  really  seen 
Jupiter's  moons ;  one  was  even  so  foolish  as  to  refuse  to 
look  through  the  telescope,  for  fear  he  should  see  them. 

Phases  of  Venus. — Galileo,  however,  now  felt  sure  that 
his  new  instrument  would  help  him  to  read  wonderful  truths 
in  the  beautiful  universe  of  God,  and  he  threw  his  whole  heart 
and  soul  into  this  grand  study.  It  was  not  long  before  he 
discovered  another  proo£jthat  the  planets  move  round  the 
sun  and  not  round  the  earth.  When  he  first  saw  the  planet 
Venu^hrougLthe..tel£scape-she  was  .rounds  but  happening 
to  Jook_  at  .her  one  day  when  she  was  almost  between  the 
earth  and  the  sun,  he  sawherjnjhe  form  of  a  crescent  like  a 
newimoon.  Struck  by  this,  he  continued  to  observe  her  night" 
after  night  till  she  had  made  the  whole  journey  round  the  sun, 
and  he  proved  to  himself  that  she  went  through  the  same 
changes  as  our  moon,  from  a  crescent  shape  to  a  full  round 
face.  This  was  just  what  she  would  be  expected  to  do  if  she 
and  we  both  travelled  round  the  sun.     Thus  for  the  second 


92 


SEVENTEENTH  CENTURY.  pt.  hi. 

time  Galileo  proved  that  the  Copernican  theory  was  the  true 
one. 

He  next  turned  his  attention  to  Saturn,  and  before  the  end 
of  the  year  he  had  made  out  that  this  planet  was  not  single, 
but  had  something  on  each  side  of  it  which  he  thought  were 
two  small  stars.  This  was  Saturn's  ring,  but  GaHleo's  tele- 
scop.ejKas_nat„p£t^er£iiLjeiLQUgh„fcr,Hn^^  ^Ih 

the  year  1659  another  famous  astronomer,  named  Huyghens, 
saw  the  ring  through  a  much  better  telescope,  and  described 
it  (see  Chapter  XXI.). 

Sun-spots. — Galileo  had  now  a  great  wish  to  go  to  Rome, 
so  that  he  might  show  the  new  wonders  he  had  discovered 
to  the  learned  men  who  lived  in  that  city.  He  accordingly 
carried  his  telescope  there  in  1611,  and  set  it  up  in  the 
Quirinal  Garden.  It  was  there  that  he  first  noticed  the  dark 
spots  on  the  face  of  the  sun,  and  observed  that  they  were 
not  always  of  the  same  shape,  but  that  two  or  three  would 
sometimes  run  into  one,  or  that  one  would  divide  itself  into 
three  or  four.  These  spots,  which  even  now  puzzle  astrono- 
mers, were  observed  by  several  other  men,  especially  by  an 
English  astronomer  named  Harriot,  about  the  same  time  as 
by  Galileo.  But  Galileo  made  a  special  use  of  his  discovery, 
for  he  pointed  out  that  the  spots  moved  round  regularly  in 
about  twenty-eight  days,  disappearing  on  one  side  of  the 
sun  and  reappearing  after  some  time  on  the  other.  This 
proved  that  the  sun  turns  round  upon  its  own  axis  in  twenty- 
eight  days. 

Galileo  before  the  Inquisition. — And  now  we  come  to 
the  sad  part  of  Galileo's  history.  He  was  well  received  in 
Rome,  and  the  Pope  even  gave  him  a  pension  of  a  hundred 
cro^vns  ;  but  the  judges  of  the  Inquisition,  who  had  caused 


CH.  XI.  GALILEO  IN  ROME.  93 

Bruno  to  be  burnt  alive,  became  uneasy  that  Galileo  should 
teach  so  many  new  things,  and  especially  that  he  should, 
prove  that  our  earth  was  not  the  centre  of  everything,  but  a 
mere  speck  among  the  numberless  stars  and  planets  in  the 
heavens.  They  therefore  sent  for  Galileo,  in  the  year  1616, 
and  threatened  to  punish  him  unless  he  would  promise  to 
hold  his  tongue  about  this  new  theory.  Galileo,  however, 
would  not* be  silent ;  surrounded  by  his  little  circle  of  admir- 
ing pupils,  he  could  not  refrain  from  spreading  wherever  he 
went  the  grand  facts  he  had  discovered  and  the  truths  they 
taught.  He  was  impatient  that  the  world  should  not  see  as 
clearly  as  he  did  how  glorious  the  universe  is  when  rightly 
understood,  and  he  often  spoke  and  wrote  sharply  and  sar- 
castically of  those  who  would  not  listen  to  truth. 

At  last,  in  1632,  he  wrote  a  book  called  '  The  System  of 
the  World  of  Galileo  Galilei,'  in  which  he  clearly  proved  the 
truth  of  the  Copernican  theory,  and  alluded  very  angrily  to 
the  attempt  which  the  Inquisition  had  made  to  force  him  to 
be  silent.  This  book  convinced  many  people,  but  at  the 
same  time  it  roused  the  anger  of  the  judges  of  the  Inquisi- 
tion. They  summoned  Galileo  (then  an  old  man  seventy 
years  of  age)  to  appear  again  before  them ;  and  this  time 
they  made  him  kneel,  clothed  in  the  sackcloth  of  a  penitent, 
and  swear  with  his  hands  upon  the  Gospels  that  '  it  was  not 
true  that  the  earth  moved  round  the  sun,  and  that  he  v,'ould 
never  again  in  words  or  writing  spread  this  damnable 
heresy.'  It  is  very  sad  to  think  that  Galileo  should  thus 
swear  to  what  he  knew  was  a  lie ;  but  it  is  still  more  sad 
that  men  holding  their  power  in  the  name  of  God  should 
force  him  to  choose  between  telling  a  lie  or  being  put  to 
torture  or  to  death  as  Giordano  Bruno  had  been.     When 


94  SEVENTEENTH  CENTURY.  pt.  hi. 

Galileo  rose  from  his  knees  it  is  said  that  he  stamped  his 
foot  and  whispered  to  a  friend  :  ^ E pur  si  muove^  ('  Never- 
theless it  does  move ') . 

After  a  time  he  was  allowed  to  go  back  to  his  own  home, 
but  never  again  to  leave  it  without  the  Pope's  permission. 
He  went  on  with  his  studies,  and  made  many  useful  obser- 
vations j  but  in  the  year  1636  his  sight  began  to  fail,  and  he 
soon  became  totally  blind.  At  this  time  he  wrote  to  an 
acquaintance  these  touching  words  :  '  Alas  !  your  dear  friend 
and  servant  has  become  totally  and  irreparably  blind.  These 
heavens,  this  earth,  this  universe,  which  by  wonderful  obser- 
vation I  had  enlarged  a  thousand  times  beyond  the  belief 
of  past  ages,  are  henceforth  shrunk  into  the  narrow  space  I 
myself  occupy.  So  it  pleases  God,  it  shall  therefore  please 
me  also.'  He  died  January  28,  1642,  in  his  seventy-eighth 
year ;  having  accomplished  his  work.  In  spite  of  all  oppo- 
sition, his  discoveries  had  firmly  established  the  truth  of  the 
Copernican  system  of  the  universe. 


Chief  Works  consulted. — Brewster's  '  Martyrs  of  Science  ; '  Drink- 
waters  *  Life  of  Galileo  ; '  Herschel's  '  Astronomy ; '  Whewell's 
'Inductive  Sciences  ;'  ' Enclyclopaedia  Britannica,'  art.  'Astronomy  ;' 
Baden  Powell's  *  Hist,  of  Natural  Philosophy;'  Ganot's  'Physics,' 
edited  by  Atkinson. 


CH.  XII.  THE  RUDOLPHINE   TABLES.  95 


CHAPTER   XII. 

SCIENCE   OF   THE    SEVENTEENTH    CENTURY    (CONTINUED). 

Kepler  the  German  Astronomer — Succeeds  Tycho  as  Mathematician 
to  the  Emperor  Rudolph — His  description  of  the  Eye — He  tries  to 
explain  the  orbit  of  the  planet  Mars — And  by  comparing  Tycho's 
tables  with  observation  discovers  his  First  and  Second  Law  of  the 
movements  of  the  Planets — His  delight  at  Galileo's  discoveries — 
Kepler's  Third  Law — Comparison  of  the  labours  of  Tycho,  Galileo, 
and  Kepler. 

Kepler,  1571-1630.— While  Galileo  was  occupied  in  dis- 
covering unknown  worlds  with  his  telescope,  another  famous 
astronomer,  named  Johannes  Kepler,  was  working  out  three 
grand  laws  about  the  movements  of  the  planets.  John 
Kepler  was  born  in  1571.  His  parents,  though  noble,  were 
poor,  and  always  in  difficulties,  but  in  spite  of  all  obstacles 
he  managed  to  educate  himself,  and  even  to  take  his  degree 
at  the  University  of  Tubingen.  In  1594  he  was  made  Pro- 
fessor of  Astronomy  at  Gratz,  in  Styria,  and  while  there  he 
began  his  attempts  to  discover  the  number,  size,  and  orbits 
of  the  planets,  but  at  first  with  no  success.  In  1597,  when 
the  Catholics  at  Gratz  rose  against  the  Protestants,  Kepler, 
being  a  Protestant,  was  forced  to  leave  the  city,  and  would 
have  been  in  great  difficulties  if  his  friend  Tycho  Brahe 
had  not  invited  him  to  come  to  Prague  as  his  assistant 
in  the  observatory.  Here  Kepler  worked  with  Tycho  at 
his  astronomical  tables,  called  the  '  Rudolphine  Tables,' 
in  honour  of  the  Emperor  Rudolph  ;  and  when  Tycho  died, 


96  SEVENTEENTH  CENTURY.  Fr.  ill. 

in  160T,  he  succeeded  him  as  principal  mathematician  to 
the  Emperor. 

Kepler  on  Optics,  1604. — Although  Kepler  is  chiefly 
known  as  an  astronomer,  his  first  work,  published  in  1604, 
was  on  Optics,  and  in  it  he  points  out  most  beautifully  the 
true  use  of  the  different  parts  of  the  eye.  He  was  much 
struck  with  Porta's  idea  that  the  eye  is  like  a  camera  obscura, 
and  he  proved  that  the  rays  of  light,  after  passing  through  the 
lens  of  the  eye,  form  a  real  picture  upside  down  on  the  fine 
network  of  nerves  called  the  retina,  at  the  back  of  the  eye, 
and  are  then  conveyed  by  the  optic  nerve  to  the  brain.  He 
also  pointed  out  that  the  reason  why  we  do  not  see  things 
upside  down  is  that  since  our  mind  follows  out  each  ray  in  a 
straight  line,  the  rays  appear  to  cross  back  again  on  the  lens 
of  the  eye,  and  we  see  them  as  if  they  had  never  been  in- 
verted. This  is,  however,  a  question  still  undecided  by 
physiologists. 

Kepler  invented  a  much  more  powerful  telescope  than 
the  one  which  Galileo  had  made.  You  will  see  by  turn- 
ing back  to  p.  88  that  the  fault  of  Galileo's  telescope  was  that 
it  made  the  rays  diverge  or  bend  outwards,  just  as  they 
reached  the  eye,  and  in  this  way  many  of  them  passed  out- 
side and  were  lost.  Kepler  avoided  this  by  using  two  convex 
lenses.  In  his  telescope  (see  Fig.  9),  the  rays  firom  the  object 
771  n,  after  converging  on  the  lens  a  b  come  to  a  focus  at  7n'  n', 
where  they  make  a  real  image  of  the  arrow  upside  down.  If 
you.  could  put  a  piece  of  thin  transparent  paper  at  the  pomt 
7n'  7i'  in  a  telescope,  you  would  see  a  picture  of  the  object 
upon  it.  The  rays  from  this  image  falling  on  the  lens  c  d, 
are  again  bent  inwards,  as  by  the  ordinary  magnifying  glass 
(see  p.  49),  and  thus  by  following  them  out  in  straight  lines 
the  eye  sees  a  niagnified  arrow  upside  down  at  some  point 


CH.  XII. 


KEPLER'S   '7HREE  LAWS: 


97 


between  c  d  and  m  n.  Kepler's  telescope  is  called  the 
'  Astronomical  telescope.'  It  has  a  much  larger  'field  of 
view '  than  Galileo's ;  that  is,  it  enables  you  to  see  over  a 
larger  space  at  one  time ;  but,  on  the    other  hand,  it  turns 

Fig.  9. 


Kepler's  Telescope.' 

A  B,  Object  glass,    c  d.  Eye-piece,     m  n.  Real  arrow,    m'  n'.  Picture  of  the  arrow 
formed  at  the  focus  of  the  rays,     m  n,  Magnified  arrow. 

everything  upside  down.  In  making  astronomical  observa- 
tions it  is  not  of  much  importance  which  part  of  a  star  is 
uppermost ;  but  for  terrestrial  telescopes  another  lens  has  to 
be  put  in  to  bring  the  images  back  to  their  right  positions, 
and  since  Kepler's  time  many  other  improvements  have  been 
made. 

Kepler's  first  Law,  1609.— After  Tycho  Brahe's  death 
Kepler  went  on  working  at  the  '  Rudolphine  Tables,'  and 
this  led  him  to  consider  again  the  movements  of  the  planets, 
and  to  try  and  find  a  theory  to  explain  the  path  or  orbit  of 
the  planet  Mars.  Mars  is  the  planet  which  stands  fourth 
from  the  sun  ;  thus  Mercury  is  nearest  to  the  sun,  then 

'  This  figure  and  also  fig.  8  were  kindly  drawn  for  me  by  Mr.  A.  R. 
Wallace. 

6 


98  SEVENTEENTH  CENTURY.  pt.  in. 

comes  Venus,  then  our  earth,  and  then  outside  our  earth  is 
Mars.  Tycho  had  noted  in  his  tables  the  places  at  which 
the  planet  had  been  seen  at  certain  periods ;  and  from  these 
observations  Kepler  calculated  where  it  ought  to  arrive  at 
other  fixed  times  if  it  moved  in  a  circle,  as  the  earlier 
astronomers  had  supposed.  But  he  found  that  it  did  not 
arrive  there  as  computed,  and  he  was  so  sure  that  Tycho's 
observations  were  exact  that  he  said  boldly, '  All  the  theories 
must  be  wrong  if  they  do  not  agree  with  what  Tycho  saw.' 
So  he  puzzled  on,  trying  one  explanation  after  another,  until 
at  last  he  discovered  three  remarkable  laws,  by  which  the 
movements  not  only  of  Mars,  but  of  all  the  other  planets, 
are  explained. 

The  first  of  these  laws  is  that  planets  move  round  the 
sun  in  ellipses  or  ovals,  and  not  in  circles.  You  know  that 
to  draw  a  circle  you  put  one  leg  of  the  compasses  into  a 
spot  and  draw  the  other  leg  round  it,  and  the  middle  spot 
is  called  the  centre  or  focus.  But  to  draw  an  ellipse  you 
must  have  two  focuses  or  foci.  To  understand  this,  stick 
two  pins  a  little  distance  apart  in  a  piece  of  paper,  and 
fasten  a  string  to  them  by  its  two  ends.  Place  a  pencil 
upright  in  the  string,  so  as  to  keep  it  tightly  stretched,  and 
draw  the  pencil  round  first  on  one  side  then  on  the  other. 
You  will  then  have  an  ellipse,  and  the  two  pin-holes  will  be 
the  two  foci.  Draw  the  sun  in  one  of  the  foci  and  a  round 
globe  on  some  part  of  the  ellipse,  and  you  will  have  a  figure 
of  the  path  of  our  earth  or  any  of  the  planets  round  the  sun. 
You  will  find  that  the  farther  you  put  the  pins  apart  the 
flatter  the  ellipse  will  be.  The  path  or  orbit  of  the  planet 
Mercury  is  much  more  elliptical  than  the  orbit  of  the  Earth. 
Another  difference  in  the  orbits  of  the  planets  is  that  they 
do  not  all  lie  in  the  same  direction,  though  they  all  have  the 
sun  as  one  of  their  foci.     For  instance  in  Fig.  lo,  the  orbit 


CH.  XII. 


KEPLER'S   'THREE  LAWS: 


99 


of  the  planet  a  has  the  sun  for  one  focus  and  the  dot  c  for ' 
the  other,  while  the  orbit  of  the  planet  b  has  the  sun  for  one 
focus  and  the  dot  d  for  the  other,  and  this  makes  the  two 
orbits  lie  in  a  different  di- 

FlG.  lO. 

rection.  Kepler's  first  law, 
then,  was  SkidX  planets  move 
in  ellipses. 

Kepler's  Second  law, 
1609. — His  second  law  was 
about  the  rate  at  which 
planets  move.  He  found 
from  Tycho's  tables  that 
they     all      moved     more 

quickly  when  they  were  near  the  sun  than  when  they  were 
far  from  it,  and  after  an  immense  number  of  calculations 
he  found  the  following  rule.  If  you  could  draw  a  line  from 
the  sun  to  any  planet  on  the  first  day  of  each  month  of 
the  year,  you  would  enclose 
a  number  of  spaces,  such 
as  ^,  by  c,  d,  &c.,  in  Fig.  1 1, 
and  each  of  these  spaces 
would  be  the  same  size, 
although  not  the  same 
shape.  For  instance,  the 
planet,  when  travelling  from 
I  to  2  near  the  sun,  would 
go  very  quickly  and  pass 
over    a   number   of  miles, 

while  when  travelling  from  6  to  7  it  would  go  slowly  and 
pass  over  comparatively  few  miles.  And  yet  the  space  / 
will  be  exactly  the  same  size  as  the  space  a,  only  it  will 
be  long  and   thin  instead  of  short  and  broad.     Kepler's 


loo  SEVENTEENTH  CENTURY.  pt.  hi. 

second  law,  therefore,  was  that  planets  describe  equal  areas 
about  their  centre  in  equal  times. 

Not  many  months  after  Kepler  published  these  two 
laws,  he  heard  of  Galileo's  discoveries  with  his  telescope — 
that  Jupiter  had  four  satellites,  and  that  Venus  was  proved 
to  move  round  the  sun  by  having  phases  like  our  moon. 
You  may  imagine  how  delighted  he  was  to  find  the  Co- 
pernican  theory  made  so  much  more  certain,  and  to  see 
that  the  telescope  was  opening  the  way  for  so  many  new 
discoveries.  *Such  a  fit  of  wonder,'  he  said,  'seized  me 
at  this  report,  and  I  was  thrown  into  such  agitation,  that 
between  the  joy  of  the  friend  who  told  me,  my  imagination, 
and  the  laughter  of  both,  confounded  as  we  were  by  such 
a  novelty,  we  were  hardly  capable,  he  of  speaking  or  I  of 
listening.' 

For  many  years  after  this  Kepler  w^as  beset  with  troubles. 
The  Emperor,  being  at  war  with  his  brother  Matthias,  had  no 
money  to  spare  for  salaries.  Kepler  was  thus  harassed  by 
poverty ;  his  favourite  son  died  of  the  small-pox,  which  the 
troops  had  brought  into  the  city,  and  his  wife  died  of  grief 
not  long  afterwards.  It  was  not  till  the  year  1618,  after  he  had 
re-married  and  had  been  rescued  from  his  poverty  by  the 
new  Emperor  Matthias,  that  the  unfortunate  astronomer  had 
energy  and  leisure  to  turn  again  to  his  favourite  planets. 

Kepler's  Third  Law,  1618. — It  was  in  that  year  that  he 
worked  out  with  immense  labour  his  third  and  most  famous 
law — by  which  he  showed  how  much  longer  the  planets  were 
going  round  the  sun,  according  as  they  were  farther  off 
from  it.  This  is  difficult  to  understand,  but  we  must  try  to 
form  some  idea  of  it.  He  did  not  know  in  figures  how  far 
each  planet  was  from  the  sun,  but  he  knew  the  proportion  of 
their  distances,  as  for  example,  that  Mars  is  4  tirnes  and 


CH.  xn.     TYCHO  BRAHE,   GALILEO,  AND  KEPLER.      loi 


Jupiter  13J  times  farther  off  from  the  sun  than  Mercury, 
and  he  also  knew  how  long  each  one  was  in  going  round  the 
sun,  and  from  these  two  facts  he  worked  the  following  rule. 

If  you  take  any  two  planets  and  cube  their  distances  from 
the  sun  and  then  square  the  time  each  takes  in  going  round 
the  sun,  the  two  squai^es  of  the  time  will  bear  the  same  pro- 
portion to  each  other  as  do  the  two  cubes  of  the  distance. 
For  instance.  Mars  is  4  times  as  far  from  the  sun  as  Mer- 
cury, and  therefore  it  is  8  times  as  long  going  round  it,  be- 
cause the  cube  of  4  (or  4  x  4  x  4)  is  64,  and  the  square 
of  8  (or  8  X  8)  is  also  64.  Thus  the  cube  of  Mercury's  dis- 
tance as  compared  with  that  of  Mars  is  i  to  64,  and  the 
square  of  their  periodic  times  of  going  round  is  also  as 
I  to  64.  This  law  holds  equally  true  of  all  the  planets,  and 
is  expressed  in  scientific  language  thus  :  '  The  squares  of  the 
periodic  times  of  the  planets  are  proportional  to  the  cubes  of  their 
distances. 

These  three  laws  of  Kepler  were  very  great  discoveries; 
especially  the  last  one,  which  cost  him  years  of  labour  and 
calculation.  He  was  so  astonished  and  delighted  when  he 
proved  it,  that  he  told  a  friend  he  thought  at  first  it  must 
be  only  a  happy  dream  that  he  should  have  succeeded  at 
last  after  so  many  failures. 

After  this  Kepler  wrote  and  published  many  books,  but 
he  made  no  more  important  discoveries.  The  Rudolph- 
ine  Tables  were  at  last  published  in  1628,  and  Kepler 
received  a  gold  chain  from  the  Grand  Duke  of  Tuscany 
for  his  services  to  Astronomy  ;  but  still  he  could  not  ob- 
tain the  payment  of  his  salary,  and  money  difficulties 
pressed  upon  him.  His  anxiety  threw  him  into  a  violent 
fever,  and  he  died  in  1630  at  sixty  years  of  age. 

Work  done  in  Science  by  Tycho  Brahe,  Galileo,  and 


I02  •        SEVENTEENTH  CENTURY.  pt.  hi. 


Kepler. — It  will  be  instructive  to  notice  here  how  very  dif- 
ferent these  three  astronomers,  Tycho,  Galileo,  and  Kepler 
were,  and  yet  how  they  each  did  their  own  part  to  add  to 
our  knowledge.  Tycho  was  a  man  who  collected  facts  :  his 
work  was  dry,  and  his  tables  a  mass  of  figures,  such  as  most 
people  would  think  very  uninteresting;  yet  if  Tycho  had  not 
spent  his  life  in  this  dry  conscientious  work,  Kepler  could 
never  have  discovered  his  laws.  Galileo  was  a  warm- 
hearted enthusiastic  observer :  he  loved  the  beauty  of  the 
heavens,  and  knew  how  to  make  others  love  it  too  j  every 
observation  he  made  he  told  in  popular  language  to  the 
world,  and  taught  people  the  truth  of  the  Copernican  theory* 
by  showing  them  plainly  how  they  could  prove  it  for  them- 
selves, if  they  chose  to  look  at  the  heavens.  Kepler  was 
quite  different  from  either  Tycho  or  Galileo ;  he  was  a  m.a- 
thematician,  and  worked  everything  out  in  his  own  brain  by 
accurate  methods.  He  took  Tycho's  observations,  which  he 
knew  were  true,  and  turned  them  this  way  and  that  way, 
working  out  now  one  calculation,  now  another,  and  always 
throwing  them  aside  if  they  were  not  exactly  true.  He  spent 
years  over  his  attempts,  but  it  was  worth  while,  for  he 
arrived  at  three  true  laws,  which  will  remain  for  ever.  There 
was  only  one  point  he  had  not  reached  \  he  knew  that  his 
laws  were  true,  but  he  did  not  know  why  they  were  true. 
This  was  left  for  Newton  to  demonstrate  nearly  fifty  years 
afterwards. 


Chief  Works  consulted. — Brewster's  'Martyrs  of  Science;'  Herschel's 

*  Astronomy ; '    Denison's   '  Astronomy  without  Mathematics  ; '  Airy's 

*  Popular    Astronomy  ;  '    Drinkwater's    '  Life    of   Kepler  ; '     Baden 
Powell's  *  History  of  Natural  Philosophy.' 


CH.  XIII.     FRANCIS  BACON.— ' NOVUM  ORGANUM:        103 


CHAPTER  XIII. 

SCIENCE   OF   THE   SEVENTEENTH    CENTURY    (CONTINUED). 

Francis  Bacon,  1561-1626 — He  teaches  the  true  method  of  studymg 
Science  in  his  'Novum  Organum' — Rene  Descartes,  1596-1650 — 
He  teaches  that  Doubt  is  more  honest  than  Ignorant  Assertion — 
Willebrord  Snellius  discovers  the  Law  of  Refraction,  1 62 1 — 
Explanation  of  this  Law. 

Bacon's  Influence  upon  Science.- — Although  this  book 
is  a  history  of  scientific  discovery  and  not  of  philosophy, 
yet  we  must  now  mention  in  passing  two  philosophers  who 
lived  about  this  time,  and  whose  writings  had  great  in- 
fluence upon  science.  These  were  Francis  Bacon  in  Eng- 
land, and  Rene  Descartes  in  France. 

Francis  Bacon,  commonly  known  as  Lord  Bacon,  was 
born  in  London  in  1561,  and  died  in  1626.  He  was  made 
Lord  Chancellor  of  England  in  16 18,  in  the  reign  of 
James  I.,  with  the  title  of  Lord  Verulam  and  afterwards 
Viscount  St.  Alban's,  and  was  a  great  political  character. 
Bacon  devoted  much  of  his  time  to  science,  and,  like  his 
namesake  Roger  Bacon  in  the  fifteenth  century,  he  seems  to 
have  foreseen  many  of  the  discoveries  which  were  afterwards 
made.  But  his  most  useful  work  was  a  book  called  the 
'Novum  Organum,'  or  'New  Method,' published  in  1620, 
in  which  he  sketched  out  very  fully  how  science  ought  to  be 
studied.  He  insisted  that  no  knowledge  can  be  real  but 
that  which  is  founded  on  experience,  and  that  the  only 


I04  SEVENTEENTH  CENTURY.  ft.  iit. 

true  way  to  cultivate  science  is  to  be  quite  certain  of  each 
step  before  going  on  further,  nor  to  be  satisfied  with  any- 
general  law  until  you  have  exhausted  all  the  facts  which  it  is 
supposed  to  explain. 

For  example,  if  you  require  to  understand  what  heat  is, 
and  how  it  acts,  you  must  not  be  satisfied,  he  says,  by 
merely  making  a  few  experiments  on  the  heat  of  the  sun  and 
that  of  fire,  and  trying  from  these  to  lay  down  some  general 
rule  of  how  heat  works.  '  No,  you  must  examine  it  in  the 
sun's  rays  both  when  they  fall  direct  and  when  they  are  re- 
flected j  in  fiery  meteors,  in  lightning,  in  volcanoes,  and  in 
all  kinds  of  flame  ;  in  heated  solids,  in  hot  springs,  in  boil- 
ing liquids,  in  steam  and  vapours,  in  bodies  which  retain 
heat,  such  as  wool  and  fur  j  in  bodies  which  you  have  held 
near  the  fire,  and  in  bodies  heated  by  rubbing;  in  sparks 
produced  by  friction,  as  at  the  axles  of  wheels  ;  in  the  heat- 
ing of  damp  grass,  as  in  haystacks ;  in  chemical  changes,  as 
when  iron  is  dissolved  by  acids  j  in  animals ;  in  the  effects 
of  spirits  of  wine ;  in  aromatics,  as  for  example  pepper, 
when  you  place  it  on  your  tongue.  In  fact,  you  must  study 
every  property  of  heat  down  to  the  action  of  very  cold  water, 
which  makes  your  flesh  glow  when  poured  upon  it.  When 
you  have  made  a  list,'  says  Bacon,  '  of  all  the  conditions 
under  which  heat  appears,  or  is  modified,  of  the  causes 
which  produce  it,  and  of  the  efiects  which  it  brings  about, 
then  you  may  begin  to  speak  of  its  nature  and  its  laws,  and 
may  perhaps  have  some  clear  and  distinct  ideas  about  it.' 

You  will  see  at  once  that  this  method  of  Bacon's  had 
been  followed  already  to  a  great  extent  by  Copernicus, 
Tycho  Brahe,  Galileo,  and  Kepler ;  but  Bacon  was  the  first 
to  insist  upon  it  as  the  only  rule  to  follow,  and  in  doing  this 
he  rendered  a  great  service  to  science. 


CH.  XIII.  WRITINGS   OF  DESCARTES.  105 

Descartes'  Condemnation  of  Ignorant  Assertion.' — Rene 

Descartes,  by  his  philosophy,  assisted  science  in  another  way. 
He  was  a  Frenchman,  born  in  Touraine  in  1596,  and  he 
became  one  of  the  most  famous  philosophers  of  France.  He 
wrote  a  great  deal  on  science,  especially  on  mathematics  and 
geometry,  and  also  on  the  nature  of  man  ;  but  the  point 
which  we  have  to  notice  here  was  his  belief  that  to  arrive  at 
the  real  truth  was  the  only  thing  worth  living  for. 

You  will  remember  how  the  men  of  science  of  the 
sixteenth  century  had  thought  it  a  sufficient  answer  to  Vesa- 
lius  or  to  Galileo  to  say  that  Galen  or  Aristotle  had  decided 
questions  of  anatomy  and  physics  ages  ago  ;  and  how  the 
judges  of  the  Inquisition  thought  they  had  crushed  the  Co- 
pernican  theory  when  they  made  Galileo  recant.  Authority 
was  the  idol  to  which  these  people  bowed  down,  and  they 
considered  it  rank  heresy  to  doubt  anything  which  had  been 
taught  by  their  forefathers.  But  Descartes  said,  '  It  is  not 
true  to  say  we  know  a  thing  simply  because  it  has  been  told 
us.  It  is  a  duty  to  obey  authority,  to  submit  to  the  laws  and 
religion  of  our  country  and  parents,  and  in  matters  where 
we  are  not  able  to  judge,  it  is  wise  to  receive  what  is  told 
us  by  those  who  know  more  than  we  do.  But  to  know 
anything  requires  more  than  this,  and  unless  the  reasons 
for  any  belief  are  so  clear  to  our  minds  that  we  cannot  doubt 
them,  we  have  no  right  to  say  we  knotu.  it  to  be  true^  but 
only  that  we  have  been  told  so.' 

I  think  you  can  see  how  this  rule  of  Descartes,  that  it  is 
often  more  honest  to  doubt  than  to  be  quite  sure  without 
good  grounds,  would  influence  science.  If  scientific  men  iri 
the  time  of  Galileo,  instead  of  saying  '  We  k?iow  that  a  heavy 
weight  falls  more  quickly  than  a  light  one  because  Aristotle 
said  so,'  had  said  more  modestly,  '  We  do  not  know^  because 


io6  SEVENTEENTH  CENTURY.  pt.  iii. 

we  have  never  tried,  but  we  think  it  probable  Aristotle  was 
right  until  someone  shows  us  that  he  was  mistaken  ; ' — if  they 
had  gone  to  the  Tower  of  Pisa  in  this  spirit,  they  would  not 
have  denied  the  truth  of  Galileo's  experiment  when  it  suc- 
ceeded before  their  very  eyes.  And  even  now,  in  the 
present  day,  you  will  see  that  the  greatest  and  best  men  who 
make  the  most  discoveries,  are  those  who  are  always  willing 
to  examine  a  new  fact,  even  though  it  may  contradict  much 
that  they  have  held  before  ;  and  who  never  pretend  to  know 
for  certain  anything  which  they  have  not  studied  with 
sufficient  care  to  be  convinced  of  its  truth. 

These  last  few  pages  may  be  rather  difficult  for  you  to 
follow,  but  the  chief  lessons  which  it  is  necessary  you  should 
remember  may  be  summed  up  in  a  few  words.  Bacon  and 
Descartes  both  did  great  service  to  Science — Bacon  by 
teaching  that  any  true  theory  must  be  built  up  upon  facts 
and  careful  experiments ;  Descartes  by  insisting  that  it  is 
more  honest  to  acknowledge  we  are  ignorant,  and  to  wait 
for  more  light,  than  to  pretend  to  know  that  which  we  have 
not  clearly  proved. 

Snellins  Discovers  the  Law  of  Refraction,  1621. — 
Among  other  things,  Descartes  wrote  much  upon  Optics,  and 
you  will  often  see  it  stated  that  he  discovered  the  law  of 
refraction.  This  law  had,  however,  been  laid  down  before, 
in  162 1,  by  a  Dutch  mathematician  named  Willebrord 
Snellius,  and  Descartes  only  stated  it  more  clearly.  You 
will  remember  that  the  Arab  Alhazen  first  pointed  out  that 
rays  of  light  are  bent  or  refracted  when  they  pass  from  a 
rarer  into  a  denser  substance  or  medium  (see  p.  47),  as  for 
instance  from  air  into  water;  and  that  the  denser  the 
medium  is  into  which  they  pass  the  more  the  rays  are  re- 
fracted.    Vitellio  and  Kepler  had  measured  some  of  the 


CH.  XIII. 


THE  LAW  OF  REFRACTION. 


107 


angles  at  which  rays  are  refracted  in  water  and  glass,  but 
they  did  not  know  of  any  law  by  which  they  could  calculate 
how  much  any  particular  ray  would  be  bent  out  of  its  course. 
For  instance,  m  Fig.  1 2,  suppose  w  w  to  be  the  surface  of 
water  in  a  glass  vessel,  upon  which  the  rays  a  and  b  fall  at 


B 


Measurement  of  Refjraction  in  Water. 

w  w,  Water,  a  a',  b  b',  Rays  passing  from  air  into  water,  d  d ,  Line  from  the  ray  a 
to  the  perpendicular  x' ,  in  the  water,  three-fourths  the  length  oi  c  c  from  the  ray  A 
in  the  air.    d  dJ ,  d  d,  Similar  lines  from  the  ray  b. 

the  point  o,  and  are  refracted  a  to  a'  and  b  to  b'.  "  It  is  evi- 
dent that  B  is  bent  much  more  out  of  its  course  than  a,  as 
you  will  see  at  once  if  you  lay  a  straight  ruler  from  end  to 
end  of  each  ray ;  and  if  we  were  to  draw  other  rays  between 
these  they  would  all  be  refracted  at  different  angles,  those 
being  most  bent  which  were  farthest  from  the  perpendicular. 
Now  in  making  telescopes  it  is  very  important  to  know 
how  much  each  ray  is  refracted  j  and  as  the  rays  are  infinite 
in  number,  it  was  impossible  to  know  this  unless   some 


io8  SEVENTEENTH  CENTURY.  pt,  hi. 


general  rule  could  be  found.  Snellius  set  himself  this  task, 
and  after  a  great  number  of  very  delicate  experiments  he 
arrived  at  a  law  which  has  proved  to  be  always  true.  This 
law  is  best  explained  by  the  following  experiment,  which  is 
not  difficult  to  understand  although  it  is  troublesome  to  per- 
form it  accurately. 

Draw  a  circle  on  a  black  board  with  an  upright  line  x  x' 
through  it,  and  then  place  the  board  upright  in  a  vessel  of 
water  so  that  the  surface  of  the  water  crosses  the  centre  o. 
Then  pass  a  ray  of  light  through  a  tube  so  placed  that  the 
ray  falls  across  the  board  in  the  direction  a  ^ ;  it  will  then 
pass  on  through  the  water  to  some  point  a'.  The  line  o  a 
will  now  cut  the  circle  at  the  point  c,  and  the  line  o  a'  will 
cut  it  at  c'.  From  these  two  points  draw  horizontal  lines  c  c 
and  dd  on  the  board  to  the  upright  line  x  x'.  Then  if  you 
compare  the  length  of  these  two  lines  you  will  find  that  d  d 
in  the  water"  is  exactly  three-fourths  of  ^  <r  in  the  air. 

Again,  if  you  throw  the  light  from  your  tube  in  the  direc- 
tion B  0,  the  result  is  the  same.  The  length  of  d'  d'  in  the 
water  will  again  be  three-fourths  of  d din  the  air.  And  this 
is  equally  true  of  all  rays  passing  from  air  into  water.  When 
a  vertical  line  is  drawn  through  the  point  where  the  ray  falls 
on  the  water,  ^/le  two  horizontal  lines  drawn  to  the  place  where 
the  circle  cuts  the  ray  will  always  be  in  the  same  propoi'tion, 
at  whatever  angle  the  ray  strikes  the  water.  Therefore,  f  ths 
is  said  to  be  the  index  of  ref7'action  for  water,  meaning  that 
every  ray  which  passes  from  air  into  water  will  have  these 
two  horizontal  lines  in  the  proportion  of  4  to  3.  In  passing 
from  air  into  glass  they  would  always  be  in  the  proportion 
of  3  to  2,  and  every  different  substance,  such  as  ice,  amber, 
diamond,  &c.,  has  its  own  angle  of  refraction.  These  have 
been  calculated,  and  tables  made,  from  which  you  can  learn 


CH.  XIII.  REFRACTION  EXPLAINED.  109 

at  once  what  is  the  index  of  refraction  for  any  particular 
substance. 

It  was  this  law  of  the  proportion  between  the  two  hori- 
zontal lines  in  the  air  and  in  the  denser  substance  which 
Snellius  discovered.  It  is  expressed  in  mathematical  lan- 
guage, thus  :  '  The  ratio  between  the  sines  of  the  ificident  and 
refracted  rays  is  always  the  same  for  the  same  substance ; ' 
sine  being  a  mathematical  term  for  the  measurement  we  have 
been  making,  which  you  will  understand  more  fully  when 
you  have  studied  trigonometry. 


Chief  Works  consulted. — Herschel's  '  Study  of  Natural  Philosophy  ;' 
Lewes's  'Biographical  History  of  Philosophy;'  Cuvier,  'Hist,  des 
Sciences  Naturelles  ; '  Bacon,  'Novum  Organum;'  Huxley  on  'Des- 
cartes,' Macmillan's  Magazine;  'Encyclopaedia  Metropolitana,'  art. 
'Light  J '  Herschel's  'Familiar  Lectures,' art.  'Light.' 


no  SEVENTEENTH  CENTURY.  pt.  iii. 


CHAPTER  XIV. 

SCIENCE   OF   THE   SEVENTEENTH   CENTURY    (CONTINUED). 

Fabricius  Aquapendente  discovers  Valves  in  the  Veins — Harvey's  dis- 
covery of  the  Circulation  of  the  Blood — Discovery  of  the  Vessels 
which  carry  nourishment  to  the  Blood — Gaspard  Asellius  notices 
the  Lacteals — Pecquet  discovers  the  Passage  of  the  fluid  to  the 
Heart — Riidbeck  discovers  the  Lymphatics. 

Harvey's  Discovery  of  the  Circulation  of  the  Blood,  1619. 

— In  the  year  1600,  when  Galileo  and  Kepler  were  still  at 
the  beginning  of  their  discoveries,  a  young  Englishman  of 
two-and- twenty,  named  Harvey,  who  was  bom  at  Folkestone 
in  1578,  went  to  Padua  to  study  anatomy  under  the  famous 
professor  Fabricius  Aquapendente.  Although  anatomists 
had  by  this  time  learnt  a  great  deal  about  the  bones  and 
parts  of  a  dead  body,  yet  they  were  still  very  ignorant  about 
the  working  of  a  Hving  one.  They  knew  that  arteries  throb, 
like  the  pulse  in  the  wrist,  which  is  an  artery  ;  and  that  veins 
(that  is,  the  blue  branching  tubes  which  you  can  see  under 
the  skin  in  your  hand  and  arm)  contain  blood  and  do  not 
throb  like  the  arteries,  but  they  had  no  clear  idea  of  the  use 
of  either  arteries  or  veins.  Vesalius  had  believed,  like 
Aristotle,  that  the  arteries  contained  chiefly  a  kind  of  air 
called  '  vital  spirits,'  which  they  carried  from  the  heart  to  all 
parts  of  the  body ;  and  that  the  blood  was  pumped  back- 
wards and  forwards  from  the  veins  to  the  heart  by  the  act  of 
breathing.     A  Spaniard  named  Servetus,  an  Italian  named 


CH.  XIV.        THE   CIRCULATION  OF  THE  BLOOD.  iii 

Columbus,  and  the  botanist  Cassalpinus,  who  all  lived  in 
the  sixteenth  century,  had  indeed  suggested  that  blood  from 
the  heart  flowed  through  the  lungs  (or  the  part  we  breathe 
with),  and  came  back  again  to  the  heart ;  and  Caesalpinus 
had  even  noticed  that  if  you  tie  up  a  vein  it  swells  on  the 
side  of  the  bandage  away  from  the  heart ;  but  the  notions 
of  all  these  men  were  very  vague  and  unsatisfactory. 

The  subject  remained  quite  obscure  till,  while  Harvey 
was  studying  at  Padua,  his  master  Fabricius  discovered  that 
many  of  our  veins  have  curious  valves  inside  them,  made 
by  the  folding  of  the  lining  of  the  vein.  These  valves,  which 
are  just  like  little  transparent  pockets,  lie  open  towards  the 
heart  so  long  as  the  blood  is  flowing  in  that  direction  ;  but 
if  you  press  on  a  vein — in  your  arm  for  instance — and 
force  the  blood  away  from  the  heart  towards  the  fingers,  the 
valves  close  at  once,  and  the  vein  swells  up  because  the 
blood  cannot  flow  on. 

Fabricius  thought  that  the,  use  of  these  valves  was  merely 
to  prevent  the  blood  escaping  too  quickly  into  the  branches 
of  the  vein  ;  but  this  explanation  did  not  satisfy  Harvey,  and 
he  determined  to  try  to  discover  which  way  the  blood 
moved  in  the  different  vessels  which  held  it  In  order  to  do 
this  he  laid  bare  the  artery  of  a  living  animal,  say  in  its  leg, 
and  tied  it  round  tight,  so  that  the  blood  could  not  flow  past 
the  bandage.  He  found  that  the  artery  became  very  full  of 
blood  and  throbbed  strongly  above  the  place  where  he  had 
bound  it,  but  in  the  lower  part  of  the  leg  it  did  not  throb 
at  all.  This  proved  to  him  that  the  blood  in  the  artery  was 
flowing  from  the  heart  to  the  leg  of  the  animal,  and  was 
stopped  on  its  way  down  by  the  bandage.  He  then  tied  up 
a  vein  in  the  same  way,  and  this  time  the  swelling  was  in 
the  lower  part  of  the  leg,  bebiv  where  the  vein  was  tied. 


ti2  SEVENTEENTH  CENTURY.  pt.  ill. 

Therefore  it  was  clear  that  the  blood  in  the  vein  was  flowing 
from  the  leg  to  the  heart,  and  was  stopped  from  flowing  up- 
wards by  the  bandage.  When  he  tied  an  artery  and  a  vein 
in  the  arm  the  same  thing  happened ;  the  blood  in  the 
artery  was  flowing  towards  the  hand,  while  in  the  vein  it  was 
flowing  _;9'<?m  the  hand  towards  the  heart. 

This  led  Harvey  to  suspect  that  the  blood  is  always 
making  a  continuous  journey  round  and  round,  first  out  of 
the  heart  through  the  arteries  to  all  parts  of  the  body,  and 
then  back  through  the  veins  to  the  heart  again.  And  now 
the  use  of  the  little  valves  became  evident.  While  the  blood 
flows,  as  it  should  do,  towards  the  heart,  they  lie  open  and 
offer  it  no  resistance,  but  directly  anything  drives  it  in  the 
v/rong  direction  they  close  at  once,  and  prevent  it  from 
flowing  backwards.  The  throbbing  of  the  arteries  was  also 
explained  by  this  theory,  for  the  blood  being  pumped  into 
them  by  a  regular  movement  of  the  heart,  they  swell  at  each 
rush  of  blood,  and  contract  again  before  the  next,  and  so 
rise  and  fall  in  exact  time  with  the  beating  of  the  heart. 

Harvey  also  found  that  Csesalpinus  and  his  contempo- 
raries had  been  right  in  suspecting  that  the  blood  makes  a 
small  circuit  from  the  heart  through  the  lungs  and  back 
again.  We  will  try  to  understand  all  this  with  the  assistance 
of  a  diagram,  which,  however,  you  must  remember  is  only 
to  help  you,  and  not  a  real  drawing  of  the  parts.  Starting 
from  the  left  lower  chamber  a  of  the  heart,  the  blood  is 
pumped  out  of  the  left  top  corner  of  this  chamber  into  an 
artery  in  the  direction  of  the  arrow  i.  This  artery  soon 
divides  into  two  branches,  one  going  downwards  by  the 
arrow  2  to  the  lower  part  of  the  body,  the  other  upwards  by 
the  arrow  2'  to  the  arms  and  neck  ;  and,  after  flowing  into 
the  different  parts  of  the  body,  the  blood  in  the  lower  arte?y 


CH.  XIV.     DOUBLE  CIRCULATION  OF  THE  BLOOD.        113 


Fig.  13. 
NECK 


LEFT 


returns  by  the  lower  vein,  while  the  blood  of  the  upper 
arte7'y  is  returning  by  the  upper  vein,  and  both  streams  pour 
into  the  right  upper  chamber  of 
the  heart,  b. 

The  blood  has  now  made  one 
round,  but  it  does  not  stop  here. 
It  escapes  through  some  valves 
down  into  the  lower  chamber  c  j 
out  of  the  right  top  corner  of 
which  it  starts  again  in  the  direc- 
tion of  arrows  8  and  9,  and  passes 
through  the  lungs,  returning  by 
the  lung- veins,  ox  pulmonary  veins 
as  they  are  called,  in  the  direc- 
tion of  arrow  10,  back  into  the 
left  top  chamber  of  the  heart,  d. 
From  there  it  passes  down  into 

the  chamber  a,  from  which  it  first    «  c.  Lower  chambers  of  the  heart, 

called    ventricles,     b    d.    Upper 

Started,  and  the  whole    round  be-  chambers   of  the    heart,    called 

auricles.     The  arrows  and  num- 

ginS  again.       The  first  journey    of         bers  show  the  course  of  the  blood. 

the  blood  round  the  whole  body  is  called  the  general  cir- 
culation, and  the  second  journey  through  the  lungs  is  called 
the  pulmonajy  circulation ;  when  Harvey  had  traced  these 
two  journeys  he  had  proved  the  double  circulation  of  the 
blood. 

Although  this  discovery  as  stated  here  appears  very 
simple,  yet  it  took  Harvey  nineteen  years  to  trace  the  blood 
through  all  the  channels  of  the  body,  before  he  felt  quite 
certain  that  he  had  hit  upon  the  truth.  Meanwhile  he  had 
returned  to  London,  and  had  been  made  physician  at  St. 
Bartholomew's  Hospital.  Here  he  taught  his  theory  in  his 
Lectures  of  16 19,  and  at  last  published  a  small  book  on  the 


Diagram  of  Heart  and  Blood-vessels 
front. 


I 


114  SEVENTEENTH  CENTURY.  pt.  hi. 

circulation  of  the  blood  in  1628.  Yet  none  of  the  older 
physicians  would  believe  he  was  right,  and  Harvey  told  a 
friend  that  he  lost  many  patients  in  consequence  of  his  new 
doctrine.  It  is  greatly  to  the  credit  of  the  unfortunate  King 
Charles  I.,  who  was  reigning  at  this  time,  and  whose  private 
physician-  rfarvey  was,  that  he  gave  him  many  opportunities 
of  making  physiological  experiments  on  the  animals  in  the 
royal  parks,  and  took  great  interest  in  his  discoveries. 
Harvey  wrote  several  other  valuable  books,  and  traced  the 
development  of  the  chicken  in  the  ^gg.  He  was  of  a  very 
gentle  and  modest  disposition,  and  disliked  controversy  so 
much  that  he  could  scarcely  be  persuaded  to  publish  his 
later  investigations  when  he  found  what  disputes  were  occa- 
sioned by  his  great  discovery  of  the  circulation  of  the 
blood.     He  died  in  1657,  in  his  eightieth  year. 

Discovery  of  the  Vessels  which  carry  Nourishment  to 
the  Blood,  1622-1649. — Harvey's  doctrine  of  the  circulation 
of  the  blood  was  the  real  starting-point  oi physiology^  or  the 
science  of  living  bodies,  and  when  the  true  action  of  the  arte- 
ries and  veins  was  known,  many  other  vessels  of  the  body  were 
soon  better  understood.  The  most  important  of  these  were 
the  vessels  which  carr}^  nourishment  from  all  parts  of  the  body 
to  make  fresh  blood.  In  1622  Gaspard  Asellius,  Professor 
of  Anatomy  at  Pavia,  saw  a  white  fluid  flowing  from  some 
thread-like  tubes  in  the  body  of  a  dog  which  he  was  dis- 
secting. This  dog  had  been  eating  food  just  before  he  died, 
and  Asellius  found  that  the  fluid  came  from  the  intestines 
and  was  the  nourishing  matter  of  the  food.  He  called  these 
fine  tubes  lacteals,  because  the  fluid  in  them  looked 
like  milk.  Some  years  later,  in  1647,  Jean  Pecquet,  an 
anatomist  of  Dieppe,  discovered  that  these  lacteals  empty 
themselves  into  a  large  tube  called  the  thoracic  duct,  which 


CH.  XIV.    FURTHER  PHYSIOLOGICAL  DISCOVERIES.     115 

carries  the  fluid  into  the  principal  vein,  and  so  to  the 
heart  j  and  finally,  in  1649,  ^  Swede  named  Olaiis  Riidbeck 
discovered  an  immense  number  of  fine  thread-like  tubes 
running  firom  all  the  principal  parts  of  the  body,  and  carrying 
nourishing  matter  to  the  thoracic  duct,  and  so  through  the 
great  vein  to  the  heart.  He  called  these  tubes  lymphatics; 
but  in  reality  the  lymphatics  and  lacteals  are  the  same 
vessels,  coming  from  different  parts  of  the  body  and  supplying 
the  material  for  new  blood.  You  will  easily  understand  that 
when  physiologists  knew  not  only  how  the  blood  circulates 
through  the  body,  but  also  how  a  fresh  supply  of  blood  is 
being  constantly  provided,  they  had  made  a  great  step 
towards  tracing  out  the  working  of  a  living  body. 


Chief  Works  consulted. — Sprengel,  *  Hist,  de  la  Medecine,'  1815  ; 
Harvey's  'Anatomical  Exercises,'  1673;  Aikin's  *  Biog.  Mem.  of 
Medicine  till  the  Time  of  Harvey,'  1780  ;  Huxley's  'Elementary  Phy- 
siology ; '  Carpenter's  '  Physiology  ; '  Kirke's  '  Physiology  ; '  Cuvier, 
'Hist,  des  Sciences,  &c.  ;'  D'Orbigny,  'Diet,  des  Sciences.' 


ii6  SEVENTEENTH  CENTURY.  pt.  hi. 


CHAPTER  XV. 

SCIENCE    OF   THE    SEVENTEENTH    CENTURY    (CONTINUED). 

Torricelli  discovers  the  reason  of  Water  rising  in  a  Pump — Uses  Mer- 
cury to  measure  the  Weight  of  the  Atmosphere — Makes  the  First 
Barometer — M.  Perrier,  at  Pascal's  suggestion,  demonstrates  varia- 
tions in  the  pressure  of  the  atmosphere — Otto  Guericke  invents  the 
Air-pump  —  Working  of  the  Air-pump  —  Guericke  proves  the 
Pressure  of  the  Atmosphere  by  the  experiment  of  the  Magdeburg 
Spheres — He  makes  the  first  Electrical  Machine — Foundation  of 
Royal  Society  of  London  and  other  Academies  of  Science. 

Torricelli's  Invention  of  the  Barometer,  1644. — We  must 
now  turn  to  quite  another  subject  on  which  new  light  was 
being  thrown  at  this  time.  Among  the  many  different 
mechanical  experiments  which  GaHleo  made  during  his  Hfe, 
there  had  been  one  with  a  common  pump  which  puzzled 
him  very  much,  and  which  he  had  never  been  able  to 
explain. 

You  know  that  if  you  put  the  mouth  of  a  squirt  in  water 
and  pull  back  the  handle,  the  water  rises  up  into  the  tube. 
That  is  to  say,  as  soon  as  you  leave  a  space  inside  the  squirt 
quite  empty  without  any  air  in  it,  the  water  rushes  in. 
In  the  same  way,  water  may  be  made  to  rise  up  a  long 
tube  standing  with  its  open  end  in  a  pond  or  basin,  by 
drawing  up  a  tight-fitting  stopper  a,  Fig.  14,  called  a  pis- 
ton, and  so  driving  the  air  out  at  the  top  and  leaving 
a  vacuum  inside  the  tube.  But  Galileo  found  that  as 
soon   as   the  water  had  risen  up  to   the   height   of  about 


CH.  XV. 


TORRICELLI—THE  BAROMETER. 


117 


Fig.  14, 


Ap 
C 


Z4-fiet 


34  feet  it  would  not  mount  any  higher,  even  though  the  tube 
between  the  surface  of  the  water  c,  and  the  piston  A,  had  no 
air  in  it.  He  could  not,  how- 
ever, find  out  why  the  water 
should  stop  rising  just  at  this 
point,  and  it  was  not  till  after 
his  death  that  his  friend  and 
follower  Torricelli  (born  1608), 
who  was  a  mathematical  pro- 
fessor at  Florence,  hit  upon 
the  reason. 

Torricelli  asked  himself, 
'  Why  does  the  water  rise  in 
the  tube  at  all?  something 
must  force  it  up.'  Then  it 
occurred  to  him  that  air  must 
weigh  something,  and  that  it 
might  be  this  weight  on  the 
open  surface  of  the  water 
which  forced  the  water  up 
the  pump  where  there  was  no 
air  pressing  it  down.  To  un- 
derstand this  you  must  picture 
to  yourself  all  the  air  round  our  globe  to  be  pressing  down 
upon  the  surface  of  the  earth.  Now,  so  long  as  the  tube 
also  is  full  of  air  the  surface  of  the  water  will  all  be  equally 
pressed  down,  and  so  will  remain  at  one  level  at  w  b  w. 
But  when  the  piston  a  is  drawn  up,  it  pushes  the  air  above 
it  out  of  the  tube,  and  so  lifts  the  weight  off  the  water  at 
B,  which  will  immediately  be  forced  up  the  tube  by  the 
pressure  of  the  air  on  the  water  outside  from  w  to  w.     This 


Section  of  a  Suction-tube. 


A,  Tight-fitting  piston,  c,  Greatest  height 
to  which  the  water  will  rise.  W  B  w. 
Natural  level  of  the  water. 


will  go  on  till  the  water  has  risen  about  34  feet  to  c  and 


ii8 


SEVENTEENTH  CENTURY. 


PT.  III. 


Fig.  15. 


then  the  column  of  water  c  b  in  the  tube  will  press  as  heavily 
on  the  water  at  b  as  the  air  does  on  the  water  outside  from 
w  to  w,  so  all  the  water  w  b  w  will  again  be  equally  pressed 
upon,  and  no  further  rise  will  take  place  in  the  tube. 

When  Torricelli  had  made  this  discovery  it  occurred  to 
him  that  if  it  was  really  the  weight  of  the  air  which  sup- 
ported the  column  of  water  it  ought   to   lift   mercury  or 

quicksilver,  which  is  fourteen 
times  heavier,  to  one-four- 
teenth of  the  height.  So  he 
took  some  mercury,  and  filling 
a  tube  A,  about  34  inches  long, 
with  it,  he  turned  the  tube 
upside  down  into  a  basin  of 
mercury,  which  being  open  was 
under  the  pressure  of  the  at- 
mosphere. The  mercury  began 
at  once  to  sink  in  the  tube,  and 
finally  settled  down  at  b,  about 
30  inches  above  that  in  the 
basin.  From  this  Torricelli 
knew  that  the  weight  of  ordi- 
nary air  is  sufficient  to  keep  a 
column  of  mercury  at  a  height 
of  30  inches  in  vacuum.  He 
had  now  therefore  made  an 
instrument  which  would  mea- 
sure the  weight  of  the  air, 
and  as  our  atmosphere  varies  in  weight  according  as  the 
weather  is  cold  or  hot,  or  damp  or  dry,  a  column  of  this 
kind  would  be  higher  when  the  air  was  heavy  and  lower 
when  it  was  light.     He  kept  this  apparatus  always  in  one 


Torricelli's  Experiment  (Ganot). 


CH.  XV.  THE   THERMOMETER.  119 

place,  and  observed  that  the  mercury  r3se  above  the  30 
inches  whenever  the  air  was  heavy,  and  sunk  below  when- 
ever the  air  was  light.  When  once  this  was  discovered  it 
was  easy  to  mark  off  inches  and  parts  of  inches  on  the  side 
of  the  tube  so  as  to  reckon  how  much  the  mercury  rose  and 
fell  each  day. 

This  was  the  beginning  of  the  barojneter,  by  which  we 
measure  the  weight  of  the  atmosphere.     It  was  a  long  time 
before  people  would  believe  that  anything  so  invisible  as  air 
could  affect  the  mercury,  but  this  was  at  last  clearly  proved 
by   a   man   named   M.  Perrier,  who   carried   a   barometer 
to   the  top  of  a   mountain  called  the  Puy  de   Dome,  in 
Auvergne.     As  the  summit  of  a  mountain  reaches  to  a  great 
height  in  the  atmosphere,  it  has,  of  course,  less  air  resting 
upon  it  than  the  valley  below  has,  and  so  the  mercury  when 
carried  to  this  height  not  being  pressed  so  much  up  the  tube, 
fell  nearly  3  inches,  and  then  rose  again  gradually  as  M. 
Perrier  came  down  into  the  valley  below  where  there  was  a 
greater  weight  of  air.     This  experiment,  which  was  suggested 
by  the  famous  French  writer  Pascal,  proved  beyond  doubt  that 
it  was  the  weight  of  the  air  which  caused  the  mercury  to  rise. 
If  now,  after  reading  this  account,  you  go  and  look  at  an 
ordinary  upright  barometer,  you  will  perhaps  be  puzzled  by 
finding  it  all  enclosed  in  wood,  and  you  will  ask  how  the 
air  can  get  to  the  mercury  to  press  it  down ;  but  if  you  look 
carefully  at  the  wooden  box  at  the  bottom,  you  will  find  a 
small  hole  in  the  wood,  often  having  a  small  plug  of  paper 
in  it  to  keep  out  the  dust,  and  through  this  hole,  even  stuffed 
up  as  it  is,  the  pressure  of  the  air  can  act.     The  space  be- 
tween the  top  of  the  column  of  mercury  (b.  Fig.  15)  and  the 
end  of  the  tube  is  a  vacuum,  or  a  space  without  any  air  in 
it,  and  is  still  called  a  Torricellian  vacuum. 


I 


I20  SEVENTEENTH  CENTURY.  pt.  hi. 

Invention  of  the  Thermometer. — The  date  of  the  in- 
vention of  the  thermometer  (or  instrument  to  measure  heat) 
is  so  uncertain  that  it  will  be  best  to  speak  of  it  here  in  con- 
nection with  the  barometer.  Galileo  is  said  to  have  made 
the  first  thermometer,  which  was  simply  a  tube  with  a  bulb 
at  the  end  standing  upside  down  in  a  basin  of  water.  The 
bulb  was  filled  with  air,  and  when  heat  was  applied  to  it,  it 
expanded  and  drove  back  the  water  in  the  tube.  A  few 
years  afterwards  a  Dutchman  named  Drebbel  made  thermo- 
meters with  spirits  of  wine  in  them,  and  finally,  in  1670, 
mercury  was  used.  Mercurial  thermometers  have  the  bulb 
and  part  of  the  tube  filled  with  mercury,  and  the  rest  of 
the  tube  is  quite  empty,  all  the  air  being  driven  out  by 
heating  the  mercury  till  it  completely  fills  the  tube,  and 
then  melting  the  end  so  as  to  close  it.  When  the  mer- 
cury cools  it  contracts  and  a  vacuum  is  left  above  it.  After- 
wards, when  the  bulb  of  this  thermometer  is  heated,  the 
mercury  expands  and  rises  in  the  tube  j  when  it  is  chilled  it 
contracts  and  falls. 

The  thermometer  was  n'ot  of  any  great  use  till  early  in 
the  eighteenth  century,  when  three  men,  Fahrenheit,  Celsius, 
and  Reaumur,  measured  off  the  tube  into  degrees,  so  that  the 
exact  rise  and  fall  could  be  known.  Celsius  and  Reaumur 
took  the  freezing-point  of  water  as  their  lowest  point ;  but 
Fahrenheit  took  the  greatest  cold  he  could  obtain  by  a  mix- 
ture of  snow  and  salt.  For  this  reason  32°  is  the  freezing 
point  of  water  in  a  Fahrenheit  thermometer,  and  his  other 
divisions  are  different  from  those  of  Celsius  or  Reaumur. 
Celsius's  scale  is  now  the  one  used  all  over  the  Continent, 
and  scientific  men  wished  to  introduce  it  into  England,  be- 
cause it  is  so  much  more  simple  than  Fahrenheit's.  It  is 
called  '  centigrade,'  or  a  hundred  steps,  because  the  freezings 


CH.  XV. 


GUERICKE—THE  AIR-PUMP. 


121 


point  of  water  is  o°,  and  the  tube  is  so  divided  that  there  are 
exactly  ioo°  degrees  between  the  freezing  and  the  boiling 
point. 

Otto  Guericke  invents  the  Air-pump,  1650 The  Tor- 
ricellian vacuum  in  the  barometer,  was  made,  as  we  have 
seen,  by  simply  fiUing  a  glass  tube  more  than  30  inches 
long  with  mercury,  and  then  turning  it  upside  down  into  a 
basin  of  the  same,  so  that  the  mercury  in  the  tube  fell  to  30 
inches,  and  an  empty  space  was  left  at  the  top.  But  in  1650, 
a  very  few  years  after  Torricelli's  experiment,  Otto  Guericke, 
a  magistrate  of  Magdeburg,  in  Prussia,  made  another  step 
in  advance  and  invented  an  au'-pump,  by  which  air  can  be 
drawn  out  of  a  vessel,  leaving  it  almost  empty.  Fig,  16  is  the 


Fig.  16. 


simplest  kind  of  air-pump,  and 
the  way  it  works  is  not  difficult 
to  understand.  At  the  bottom 
is  a  glass  jar  which  has  a 
round  barrel  or  cylinder,  b  b, 
fixed  on  the  top  of  it.  In  the 
cylinder  is  a  tight-fitting  piston, 
c  c,  like  the  one  in  the  suc- 
tion-tube p.  117,  only  that  this 
one  has  in  it  a  valve  or  door, 
d.  There  is  also  another 
valve,  e,  at  the  place  where  the 
cylinder  and  glass  jar  meet, 
and  both   these  valves   open 

Air-pump  (Knight), 
upwards.        Now     suppose     we    i, «,  Cylinder,      .c.  Piston  with  a  valve. 
start     with     both     valves      shut  ^^,Valves  opening  upwards. 

and  the  piston  c  c  down  at  the  bottom  of  the  cyHnder  rest- 
ing on  the  valve,  e.  Then  if  we  pull  the  piston  gradually 
up,  the  valve  d  will  be  kept  shut  by  the  air  outside  pressing 

r 


122  SEVENTEENTH   CENTURY.  pt.  hi. 

upon  it,  and  so  the  piston  will  force  the  air  between  b  and 
B,  out  of  the  top  of  the  cylinder.  If  the  valve  e  remained 
also  shut  there  would  now  be  a  vacuum,  or  space  without 
air,  in  the  cylinder  b  j  but  this  will  not  be  so,  because 
the  air  in  the  jar  below,  being  no  longer  kept  down  by  air 
above  it,  will  expand,  and  forcing  up  the  valve  e  will  fill  the 
whole  of  the  jar  and  the  cylinder  with  expanded  air. 

Now  bring  down  the  piston  c  c  again  and  observe  what 
will  happen.  The  thin  air  in  the  cylinder  will  be  pressed 
down  upon  the  valve  e  and  will  shut  it,  and  then,  not  being 
able  to  get  down  into  the  jar,  it  will  force  up  the  valve  d 
again,  and  escape  out  at  the  top.  The  piston  will  now  be 
resting  once  more  upon  the  valve  e  ;  but  the  glass  jar  will 
have  much  less  air  in  it  than  it  had  at  first,  because  it 
will  have  lost  all  that  which  went  up  into  the  cylinder  and 
was  pressed  out  at  the  top.  You  have  only  to  repeat  this 
process  and  more  air  still  will  be  drawn  out,  and  thus  by 
moving  the  piston  up  and  down  you  gradually  empty  the 
glass  jar.  You  cannot  get  quite  all  the  air  out,  because 
there  must  be  enough  left  to  push  open  the  valve  ^  when 
you  pull  the  piston  up,  but  you  can  go  on  till  there  is 
very  little  indeed.  Air-pumps  are  now  constructed,  by  which 
the  air  can  be  entirely  drawn  out  and  a  perfect  vacuum 
left ;  but  we  are  speaking  of  the  one  Guericke  niade,  which 
was  like  the  one  I  have  described,  only  more  complicated, 
and  he  worked  it  under  water  to  make  quite  sure  that  no 
air  should  creep  in  at  the  cracks. 

The  Experiment  of  the  Magdeburg  Hemispheres. — 
The  first  experiment  which  Guericke  made  with  his  air- 
pump  was  to  prove  that  the  atmosphere  round  our  earth  is 
pressing  down  upon  us  heavily  and  equally  in  all  directions. 
To  do  this  he  took  two  hollow  metal  hemispheres,  like  the 


CH.  XV.         THE  FIRST  ELECTRICAL  MACHINE,  12: 


two  halves  of  an  orange  with  the  inside  taken  out.     These 
hemispheres  fitted  tightly  together,  so  that  no  air  could  pass 
in  or  out  when  they  were  shut.     Outside  he  fastened  rings 
to  hold  by,  so  as  to  pull  them  apart,  and  at  the  end  of  one 
hemisphere  he  fixed  a  tap  which  fitted  on  to  his  air-pump. 
Now,  as  long  as  there  was  air  inside  the  closed  globe  the 
two  halves  came  apart  quite  easily ;  but  when  he  had  drawn 
out  the  air  with  the  air-pump  and  turned  off  the  tap  so  as  to 
leave  a  vacuum  inside,  it  required  immense  strength  to  drag 
the  globe  into  two  parts.     This  showed  that  the  atmosphere 
was  pressing  heavily  on  every  side  of  the  globe,  forcing  the 
two  halves  firmly  together,  and  as  there  was  no  air  inside  to 
resist  this  pressure,  the  person  trying  to  separate  them  had 
to  force  back,  as  it  were,  the  whole  weight  of  the  atmo- 
sphere to  get  them  apart.     As  Guericke  was  burgomaster  of 
Magdeburg,  this  experiment  has  always  been  called  '  the  ex- 
periment of  the  Magdeburg  hemispheres.' 

The  first  Electrical  Machine  made  by  Guericke. —You 
will  remember  that  Gilbert  had  shown  in  1600  that  sulphur 
and  many  other  bodies,  when  they  are  rubbed,  will  attract 
light  substances.  Since  his  time  very  little  notice  had  been 
taken  of  this  fact,  till  Guericke  invented  the  first  rough  elec- 
trical machine  in  1672.  He  made  a  globe  of  sulphur  which 
turned  in  a  wooden  frame,  and  by  pressing  a  cloth  against 
it  with  his  hand  as  it  went  round  he  caused  the  sulphur  to 
become  charged  with  electricity.  His  apparatus  was  very 
rough,  but  it  led  to  better  ones  being  made ;  and  some 
years  later,  in  1740,  a  man  named  Hawksbee  substituted  a 
glass  globe  for  the  sulphur  and  a  piece  of  silk  for  the  cloth, 
and  in  this  way  electrical  machines  were  made  much  like 
those  we  now  use. 

Guericke  also  discovered  that  bodies  charged  with  the 


124  ■     SEVENTEENTH  CENTURY,  pt.  hi. 

same  kind  of  electricity  repel  each  other.  If  you  hang  a 
piece  of  paper,  or  better  still,  a  pith  ball  ^,  upon  a  silk 
thread  b^  and  hold  near  to  it  a  piece  of  sealing-wax  c  rubbed 
with  dry  flannel,  you  will  find  that  the  ball  will  at  first  be 
attracted  towards  the  seaHng-wax  as  in  i,  Fig.  17,  but  after  a 
few^  moments  it  will  be  repelled  and  will  draw  back  as  in  2  ; 
nor  mil  it  approach  the  sealing-wax  again  till  it  has  been  near 
some  other  body,  and  given  up  part  of  the  electricity  it  has 
received.     Thus  an  electrical  body,  as  Guericke  pointed  out, 


Pith-ball,  attracted  and  repelled  by  rubbed  sealing-wax. 

attracts  one  that  is  not  electrified,  but  repels  it  again  as  soon 
as  it  has  filled  it  with  electricity  like  itself.  He  was  also  the 
first  to  notice  the  spark  of  fire  and  crackling  sound  which 
are  produced  by  electricity  when  it  passes  between  two 
bodies  which  do  not  touch  each  other. 

Foundation  of  the  Royal  Society  of  London  and  other 
Academies  of  Science,  1645. — We  must  now  return  to  Eng- 
land, where  about  this  time  an  event  took  place  which, 
though  it  seemed  insignificant  at  the  time,  had  in  the  end  a 
great  influence  upon  science.  In  the  year  1642  the  unfor- 
tunate King  Charles  I.  began  that  civil  war  with  his  people 
which  ended  in  his  being  beheaded  on  January  30,  1649. 
During  these  years  all  England  was  in  a  state  of  turmdil  and 
confusion,  and  in  London  especially  the  riots  and  disturb- 


CH.  XV.     FOUNDATION  OF  THE  ROYAL   SOCIETY.      125 

ances  made  it  almost  impossible  for  quiet  and  studious 
people  to  live  in  peace.  It  was  under  these  circumstances 
that  a  small  group  of  scientific  men,  among  whom  were 
Robert  Boyle,  son  of  the  Earl  of  Cork,  and  Dr.  Hooke,  an 
eminent  English  mathematician,  began  to  meet  together 
privately  to  try  and  forget  public  troubles  in  discussing 
science.  They  assembled  first  in  London  in  1645,  t»ut  soon 
moved  to  Oxford  to  be  out  of  the  way  of  the  constant  riots, 
and  continued  to  meet  there  till  1662,  after  the  restoration 
of  Charles  II.,  when  they  settled  in  London  and  formed 
themselves  into  a  regular  Society  under  a  charter  from  the 
king. 

This  was  the  beginning  of  the  Royal  Society  of  London, 
which  has  done  so  much  for  science  during  the  last  two  hun- 
dred years,  and  which  is  still  the  leading  scientific  society  of 
England.  The  following  account  of  its  early  meetings  is  thus 
given  by  Dr.  Wallis,  one  of  the  first  members, '  Our  business,' 
he  says,  'was  (precluding  matters  of  theology  and  State 
affairs)  to  discourse  and  consider  of  philosophical  enquiries, 
and  such  as  related  thereunto  :  as  Physick,  Anatomy, 
Geometry,  Astronomy,  Navigation,  Staticks,  Magneticks, 
Chymicks,  Mechanicks,  and  Natural  Experiments  ;  with  the 
state  of  these  studies,  and  their  cultivation  at  home  and 
abroad.  We  then  discoursed  of  the  circulation  of  the  blood, 
the  valves  in  the  veins,  the  venae  lactae,  the  lymphatic  vessels, 
the  Copemican  hypothesis,  the  nature  of  comets  and  new 
stars,  the  satellites  of  Jupiter,  the  oval  shape  (as  it  then 
appeared)  of  Saturn,  the  spots  on  the  sun  and  its  turning  on 
its  owTi  axis,  the  inequalities  and  selenography  of  the  moon, 
the  several  phases  of  Venus  and  Mercury,  the  improvement 
of  telescopes  and  grinding  of  glasses  for  that  purpose,  the 
weight  of  the  air,  the  possibiHty  or  impossibility  of  vacuities 


126  SEVENTEENTH  CENTURY.  pt.  hi. 

and  Nature's  abhorrence  thereof,  the  Torricellian  experiment 
in  quicksilver,  the  descent  of  heavy  bodies  and  the  degrees 
of  acceleration  therein,  with  divers  other  things  of  like 
nature,  some  of  which  were  then  but  new  discoveries,  and 
others  not  so  generally  known  and  embraced  as  they  now 
are ;  with  other  things  appertaining  to  what  hath  been 
called  the  New  Philosophy,  which,  from  the  times  of  Galileo 
at  Florence  and  Sir  Francis  Bacon  (Lord  Verulam)  in 
England,  hath  been  much  cultivated  in  Italy,  France,  Ger- 
many, and  other  parts  abroad,  as  well  as  with  us  in  Eng- 
land.' 

How  well  we  can  picture  from  this  account  (written 
in  1696),  the  pleasure  which  this  little  group  of  men, 
weary  of  the  quarrels  and  bloodshed  of  the  times,  felt  in 
discussing  and  investigating  those  laws  of  nature  which  seem 
to  bring  us  into  the  calm  presence  of  an  Almighty  Un- 
changing Power  far  above  the  petty  wranglings  of  man  ! 
The  Royal  Society  has  become,  as  I  have  said,  one  of  the 
grandest  scientific  bodies  in  the  world ;  but  it  has  probably 
never  held  more  earnest  or  enthusiastic  meetings  than  in  the 
small  lodgings  at  Oxford  where  it  first  took  its  rise  in  the 
midst  of  civil  war. 

England  was  not  long  the  only  country  which  had  a 
scientific  society.  Italy  had  already  had  two  in  the  time  of 
Galileo  and  Torricelli,  but  they  had  soon  been  broken  up 
again.  In  Germany,  the  '  Imperial  Academy  of  the  Curious 
in  Nature'  was  founded  in  1662;  and  in  1666  the  famous 
'French  Academy  of  Sciences'  was  legally  established  by 
the  French  Government  in  Paris. 

All  these  societies  were  a  great  help  in  spreading  the 
knowledge  of  scientific  discoveries.  Men  who  before  were 
unable  to  publish  what  they  knew,  now  sent  or  read  their 


CH.  XV.  EARL  V  MEMBERS  OF  THE  RO  YAL  SOCIETY.     127 


papers  to  those  who  could  understand  and  appreciate  them. 
The  Royal  Society  began  from  the  first  to  publish  useful 
memoirs  in  their  Philosophical  Transactions  ;  and  in  1669 
we  find  them  bringing  out  the  works  of  an  ItaHan  anatomist, 
Malpighi,  of  whom  we  shall  speak  presently,  and  who  sent 
to  them  works  which  he  could  not  afford  to  publish  in  Italy. 
By  this  means  the  information  scattered  about  the  world 
was  gathered  together,  and  men  were  encouraged  to  seek 
out  new  truths  when  there  w^as  a  chance  of  their  being 
known  and  appreciated. 

Among  the  earlier  members  of  the  Royal  Society  there 
were  some  whose  discoveries  we  must  now  consider.  These 
were  Boyle  and  Hooke,  whom  we  have  already  mentioned  ; 
John  Mayow,  whose  experiments  in  chemistry  are  especially 
interesting ;  Ray,  Grew,  and  Malpighi,  naturalists  and  ana- 
tomists ;  the  Dutch  astronomer  Huyghens ;  the  English 
astronomer  Halley,  and  last,  but  not  least,  England's  great 
philosopher,  Sir  Isaac  Newton. 


Chief  Works  consulted.  —  Ganot's  'Physics,'  1873;  Balfour  Stewart 
on  'Heat,'  1871  ;  Rossiter's  'Physics,'  1870 ;  Baden  Powell's  'Hist- 
tory  of  Nat.  Philosophy,'  &c.  ;  Cuvier,  *  Histoire  des  Sciences,'  &c.  ; 
Birch's  *  Hist,  of  Royal  Society  ;'  Thomson's  '  Hist,  of  Royal  Society,' 
1812. 


128  SEVENTEENTH  CENTURY.  pt.  hi. 


CHAPTER   XVI. 

SCIENCE    OF   THE    SEVENTEENTH    CENTURY   (CONTINUED). 

Boyle's  Law  of  the  Compressibility  of  Gases — This  same  Law  dis- 
covered independently  by  Marriotte — Hooke's  theory  of  Air  being 
the  cause  of  Fire — Boyle's  experiments  with  Animals  under  the 
Air-pump — John  Mayow,  the  greatest  Chemist  of  the  Seventeenth 
Century — His  experiments  upon  the  Air  used  in  Combustion — 
Proves  that  the  same  portion  is  used  in  Respiration  — Proves  that 
Air  which  has  lost  its  Fire-air  is  Lighter — Mayow's  '  Fire-air '  was 
Oxygen,  and  his  Lighter  air  Nitrogen — He  traces  out  the  effect 
which  Fire-air  produces  in  Animals  when  Breathing. 

Boyle's  Law  of  the  Compressibility  of  Gases,  1661. — The 
Hon.  Robert  Boyle,  seventh  son  of  the  Earl  of  Cork,  and 
one  of  the  principal  founders  of  the  Royal  Society,  was  bom 
in  1626.  He  had  very  delicate  health,  and  when  quite 
young  travelled  much  abroad  and  learned  there  a  great  deal 
about  science  even  before  he  was  eighteen  years  of  age.  He 
was  deeply  interested  in  Galileo's  discoveries,  and  was  in 
Florence  when  that  great  astronomer  died  in  1642. 

After  his  return  to  England,  when  he  was  at  Oxford,  he 
read  an  account  of  Guericke's  air-pump,  and  was  so  de- 
lighted with  this  new  discovery  that  he  set  to  work  at  once 
to  make  one  without  ever  having  seen  the  original.  He 
succeeded  so  well,  with  the  help  of  his  friend  and  assistant 
Dr.  Hooke,  that  his  air-pump  became  famous,  and  many 
writers  have  by  mistake  given  him  the  credit  of  being  the 


CH,  XVI. 


COMPRESSIBILITY  OF  GASES. 


129 


Fig.  i8. 


inventor.  We  have  seen,  however,  that  Guericke  was  the 
first  to  hit  upon  this  instrument ;  Boyle  only  improved  it, 
and  made  with  it  many  very  valuable  experiments  upon  the 
weight  and  nature  of  air.  These  are  too  many  and  lengthy 
for  us  to  examine  here  ;  but  there  is  one  law  about  the  com- 
pression of  gases  which  you  will  find  connected  with  Boyle's 
name  in  all  books  on  physics,  and  which  you  ought  to  under- 
stand. Boyle  knew  from  Torricelli's  experiment  that  the 
weight  of  the  atmosphere  upon  the  air,  close  down  to  our 
earth  is  about  equal  to  the  weight  of  30  inches  of  mercury  in 
a  tube  (see  p.  118).  Now  he 
wished  to  find  out  how  much 
air  is  compressed,  or  forced  into 
a  smaller  space,  when  more 
weight  is  put  upon  it,  and  to 
prove  this  he  devised  the  fol- 
lowing experiment.  He  took 
a  tube  A*,  open  at  the  long 
end  and  full  of  ordinary  air, 
and  by  putting  a  little  mercury 
into  the  tube  and  shaking  it 
carefully  till  it  settled  at  the 
bottom,  he  cut  off  a  small  quan- 
tity of  air  between  b  and  c. 
This  air  was  of  course  still  un- 
der the  usual  weight  of  the  at- 
mosphere, which  pressed  dowTi 
upon  the  mercur}'^  through  the 
open  end  of  the  tube.  But 
the   mercury  did  not  add  to      » 

the  weight  because   it  stood  at  the  same  height  on  both 
sides  of  the  tube,  and  so  was  evenly  balanced. 


Fressure 

AtmospJiere 
equals 


1Z 


-jQ 


Pressure 

of 
Msrcury 


-t30 


25 


-20 


Its 


--70 


30 


\--io 


I30  SEVENTEENTH  CEATUJRY.  pt.  III. 

He  next  added  more  mercury,  till  it  stood  30  inches  higher 
in  the  long  end  than  in  the  short  one  (as  seen  in  a*-*).  The 
air  between  b  and  c  was  now  pressed  down  twice  as  much  as 
before,  for  it  had  the  30  inches  of  mercury  weighing  upon 
it,  as  well  as  the  atmosphere,  which  equalled  another  30 
inches.  Boyle  found  that  this  double  pressure  had  squeezed 
it  into  half  the  space  {b  c,  fig.  a^)  ;  in  other  words,  by 
doubling  the  pressure  he  had  halved  the  volume  of  the  air. 
He  then  poured  in  30  inches  more  mercury,  making  the 
pressure  three  times  as  great  as  at  first,  and  he  found  the  air 
was  now  compressed  into  one-third  of  the  space  it  had  filled 
at  first.  And  this  he  proved  to  be  the  law  of  compression  of 
air  and  of  all  gases,  that  the  volume  of  a  gas  (that  is,  the 
space  it  fills)  is  decreased  in  proportion  as  the  weight  upon  it  is 
increased.  If  you  double  the  pressure  you  halve  the 
vohime  j  if  you  halve  the  pressure  you  double  the  volume. 

This  law  of  the  compressibility  of  gases  is  known  as 
Boyle^s  Law,  or  sometimes  as  Marriotte^s  Law,  because  a 
Frenchman  named  Marriotte  also  discovered  it  some  years 
later  without  knowing  that  Boyle  had  done  so.  It  is  not 
always  absolutely  true,  but  we  cannot  stop  to  discuss  the 
exceptions  here  ;  you  will  find  them  in  books  on  physics  and 
chemistry. 

Boyle  and  Hooke  both  gave  much  time  to  the  study  of 
chemistry.  Hooke  published  a  theory  in  1665  that  air  acts 
upon  substances  when  they  are  heated,  and  so  produces  fire  ; 
for,  said  he,  in  making  charcoal,  although  the  wood  is  in- 
tensely heated  and  glows  brightly,  yet  so  long  as  the  air  is 
kept  away  it  will  not  be  consumed.  Boyle  also  proved  that 
a  candle  will  not  bum,  nor  animals  breathe,  without  air. 
He  found  that  when  he  put  mice  and  sparrows  into  his  air- 
pump,  and  then  drew  out  the  air,  they  died ;  and  that  flies, 


CH.  XVI.  JOHN  MAYOW.  131 

bees,  and  even  worms,  became  insensible ;  while  fish, 
though  they  lived  longer  than  the  mice,  soon  turned  on  their 
backs  and  ceased  to  live.  He  also  put  a  bird  under  a  glass 
vessel  full  of  air,  and  it  died  after  three-quarters  of  an  hour. 
It  was  clear,  therefore,  that  fresh  air  is  necessary  to  life,  and 
Boyle  began  to  think  that  just  as  a  candle-flame  cannot  be 
kept  up  without  air,  so  there  must  be  some  vital  fire  in  the 
heart  which  is  extinguished  when  air  is  shut  out  from  it. 

This  opinion  he  discussed  at  the  Oxford  meetings,  and  a 
young  physician  named  John  JMayow  listened  very  eagerly, 
and  then  went  home  and  set  himself  to  try  and  find  out  what 
this  strange  power  in  the  air  could  be,  without  which  neither 
fire  nor  animals  could  exist. 

Mayow's  Experiments  on  Respiration  and  Combustion, 
1645-1679. — John  Mayow's  private  history  is  very  short. 
He  was  born  in  Cornwall  in  1645  i  ^^  became  a  Fellow  of 
All  Souls',  Oxford,  and  practised  as  a  physician  in  Bath  ;  and 
finally  he  died  at  the  house  of  an  apothecary  in  York  Street, 
Covent  Garden,  in  1679,  before  he  was  thirty-four  years  of 
age.  This  is  all  we  know  about  his  life  ;  but  he  must  have 
been  a  diligent  worker  and  a  real  lover  of  science,  for  though 
he  died  so  young  he  left  behind  him  an  account  of  a  number 
of  experiments  and  discoveries  which  entitle  him  to  be  called 
the  greatest  chemist  of  the  seventeenth  century.  I  wish  we 
could  go  through  all  his  experiments,  for  they  form  a  most 
beautiful  lesson  of  the  earnest  and  painstaking  way  in  which 
God's  laws  should  be  investigated.  Mayow  never  made  a 
careless  experiment ;  he  never  thrust  in  his  own  guesses 
when  it  was  possible,  to  work  out  the  truth ;  he  went  on 
patiently  step  by  step,  taking  every  care  to  avoid  mistakes, 
and  never  resting  till  he  had  got  to  the  bottom  of  his 
difficulties.     Let  us  now  take  some  of  his  experiments  on 


132 


SEVENTEENTH  CENTURY. 


PT.  III. 


combustio7tj  or  burning,  and  respiration,  or  breathing,  and  try 
and  follow  them  as  carefully  as  he  did. 

It  seemed  to  him  clear  from  the  experiments  of  Boyle 
and  Hooke  that  there  must  be  something  in  the  air  which 
gave  rise  to  flame  and  breath,  and  that  this  could  only  be  a 
small  part  of  the  air,  since  a  candle  when  put  under  a  bell- 
glass  went  out  long  before  all  the  air  was  gone.  He  first  of 
all  satisfied  himself  by  experiments  that  this  gas  which 
burnt,  and  which  he  called  fire-air,  was  not  only  in  the 
atmosphere,  but  existed  in  nitre,  or  saltpetre,  and  also  in 
many  acids ;  and  then  he  set  to  work  to  discover  how  much 
of  it  there  was  in  ordinary  air.  To  do  this  he  took  a  piece 
of  camphor,  with  some  tinder  dipped  in  melted  sulphur, 
and  placed  it  on  a  little  platform  hung  inside  a  bell-jar  (see 
Fig.  19).  He  then  lowered  the  bell-jar  into  a  basin  of  water, 
having  first  put  a  siphon  or  bent  tube  under  the  bell-jar  to 
let  enough  air  out  for  the  water  to  rise.  Then  he  took  the 
tube  out,  leaving  the  water  at  the  same  height  inside  and 
outside  the  jar,  while  the  rest  of  the  jar  above  the  water  was 

Fig.  19.  Fig.  20. 


Mayow's  experiments  on  combustion  and  respiration  (YeatsX 

full  of  air.  He  now  held  up  a  burning-glass,  and  brought 
the  sun's  rays  to  a  focus  upon  the  camphor  and  tinder  till  it 
grew  hot  and  burst  into  a  flame.     As  it  burnt  he  noticed  that 


CH.  XVI.  RESPIRATION  AND   COMBUSTION.  133 


at  first  the  water  inside  the  jar  sank  down,  because  the  air, 
being  heated,  expanded  and  took  up  more  room.  Then  after 
a  time  the  camphor  ceased  to  burn,  the  jar  cooled  down,  and 
the  water  rose  again  higher  than  before,  till  it  stood  above  the 
water  outside.  The  camphor  was  not  all  consumed,  but 
when  he  tried  to  light  it  again  he  could  not  succeed.  Why 
was  this  ?  '  Because,'  said  Mayow,  '  there  are  no  fire-air 
particles  left  in  the  jar  to  make  the  camphor  burn,  and  the 
using  up  of  these  particles  has  made  the  rest  of  the  air  shrink 
and  take  up  less  space.' 

He  now  wished  to  compare  burning  with  breathing,  so 
he  put  a  mouse  in  a  cage  and  hung  it  inside  the  bell-jar, 
which  he  arranged  over  the  water  as  before.  Little  by  little 
as  the  mouse  breathed  the  water  crept  up  inside  the  jar,  until 
when  it  had  risen  to  a  certain  height  the  mouse  drooped  and 
died.  It  was  clear,  therefore,  that  animals  in  breathing  use 
up  some  portion  of  the  air.  But  is  it  the  same  portion  which 
the  flame  uses  ?  Many  people  would  have  jumped  at  this 
conclusion,  but  Mayow  was  not  content  till  he  had  proved 
it  by  another  experiment.  He  put  a  lighted  candle  and  a 
mouse  together  inside  the  bell-jar.  The  water  now  rose 
much  faster  than  before  ;  the  candle  went  out  first,  and  then 
the  mouse  drooped  as  soon  as  the  water  had  risen  to  the 
same  height  as  in  the  other  experiment.  He  was  now 
certain  that  the  candle  and  mouse  both  used  up  the  same 
fire-air  particles  ;  but  to  make  still  more  sure,  he  put  a  candle 
under  a  bell-jar  where  the  air  had  been  spoiled  by  breathing, 
and  it  went  out  directly. 

His  next  step  was  to  try  whether  air  was  lighter  or 
heavier  after  the.  fire-air  had  been  used  up.  To  do  this  he 
put  two  mice  into  the  jar,  one  at  the  top  and  the  other  at 
the  bottom  j  the  one  at  the  top  drooped  and  died,  while  the 


134  SEVENTEENTH  CENTURY.  PT.  ill. 

other  was  still  breathing.  This  proved  that  the  air  which 
had  lost  \\.'s> fire-air  particles  was  lightest  and  "rose  to  the  top, 
so  that  the  top  mouse  could  no  longer  breathe.  By  these 
and  a  great  many  other  experiments  Mayow  proved  that  air 
is  made  up  of  two  portions — one  heavy,  which  supports  flame 
and  life  ;  the  other  light,  and  which  is  useless  for  burning  or 
breathing,  and  this  last  was  the  largest  portion.  I  want  you  to 
notice  this  particularly,  because  you  will  see  by-and-by  that 
Mayow  had  really  discovered  and  described  two  gases.  The 
one  which  he  called yfr^-^/r  was  oxygen^  which  was  not  known 
to  other  chemists  for  more  than  one  hundred  years  later,  and 
the  other  and  lighter  one  is  now  called  nitrogen. 

Having  now  proved  that  an  animal  in  breathing  uses  up 
the  same  part  of  the  air  which  a  candle  does  in  burning, 
Mayow  wanted  next  to  know  what  this  fire- air  did  inside  the 
animal.  Harvey,  as  you  remember,  had  proved  that  the 
blood  passes  through  the  lungs  and  there  meets  the  air  which 
we  draw  in  at  each  breath.  Here  then,  said  Mayow,  the 
fire-air  particles  must  come  in  contact  with  the  blood,  and, 
joining  with  it  in  the  same  way  as  they  do  with  the  fat  of 
a  candle,  must  cause  the  heat  of  the  blood.  If  anyone  wants 
to  prove  this  let  him  run  fast.  He  will  find  that  he  is  obliged 
to  breathe  more  quickly  and  draw  more  air  into  his  lungs, 
which  will  soon  make  his  blood  hotter  and  move  more 
quickly,  till  his  whole  body  glows  with  warmth.  But  if  this 
mixture  of  the  air  with  the  blood  does  really  take  place,  the 
arteries  into  which  blood  has  just  flowed  from  the  lungs  and 
heart  ought  to  be  full  of  air ;  and  this  is  easily  proved  to 
be  the  case  by  putting  warm  arterial  blood  under  an  air- 
pump,  where,  as  soon  as  the  pressure  of  the  outside  air  is 
taken  off,  innumerable  bubbles  rise  out  of  the  blood  as  fast 
as  they  can  come. 


CH.  XVI.     BECHER  AND   STAHL—' PHLOGISTON:  135 

In  this  way,  by  careful  experiments  and  reasoning 
Mayow  succeeded  in  proving  that  fire-ah'  (or  oxygen)  is 
the  chief  agent  in  combustion  and  respiratmi.  If  he  had 
not  died  so  young  he  might  have  become  more  known,  and 
men  might  have  studied  his  discoveries,  which  he  pubHshed 
in  1674.  Unfortunately,  however,  he  did  not  live  to  spread 
his  knowledge,  and  a  false  theory  of  combustion  caused  his 
work  to  be  forgotten  for  many  a  long  year. 

Theory  of  *  Phlogiston,'  1680-1723.— This  mistaken 
theory  was  proposed  by  two  very  eminent  chemists,  John 
Joachim  Becher  (1625-1682)  and  Ernest  Stahl  (1660- 
1734).  Ernest  Stahl  in  particular  was  a  man  of  great 
talent  and  perseverance,  and  he  did  a  great  deal  for  the 
study  of  chemistry  by  collecting  a  great  number  of  facts 
about  the  way  in  which  different  substances  combine  to- 
gether, and  by  arranging  these  facts  into  a  system.  But  his 
theory  of  combustion  was  quite  mistaken,  and  it  seems  very 
surprising  that  it  should  have  been  received  by  the  chemists 
of  that  day  in  the  face  of  the  facts  so  carefully  proved  by 
Mayow.  Stahl  imagined  that  all  bodies  which  would  bum 
contained  an  invisible  substance  which  he  called  ^Phlo- 
giston^ and  that  when  a  body  was  burnt  it  gave  up  its 
phlogiston  into  the  air,  and  could  only  regain  it  by  taking  it 
out  of  the  air  or  some  other  substance.  It  would  only  con- 
fuse you  to  try  and  understand  how  this  theory  explained 
some  of  the  facts  of  chemistry.  You  will  see  at  once  one 
which  it  did  not  explain,  namely,  why  a  body  should  grow 
heavier  when  it  is  burnt,  as  Geber,  1,500  years  before,  had 
shown  it  does.  This  fact  alone  ought  to  have  been  sufficient 
to  prevent  the  theory  gaining  ground ;  but  Stahl's  fame  was  so 
great,  and  his  imaginary  '  Phlogiston '  seemed  to  answer  so 
well  in  a  gi*eat  many  problems,  that  chemists  believed  in  it 


136  SEVENTEENTH  CENTURY.  pt.  hi. 

for  nearly  a  hundred  years,  and  Mayow's  true  explanation 
was  forgotten  till  the  eighteenth  century,  when  fresh  experi- 
ments proved  Stahl's  theory  to  be  false.  ^ 


Chief  Works  consulted. — Brande's  'Manual  of  Chemistry' — Intro- 
duction ;  Rodwell's  '  Birth  of  Chemistry  ; '  Yeats  '  On  Claims  of 
INfodems  to  discoveries  in  Chemistry  and  Physiology,'  1798;  Birch's 
*  Life  of  Boyle,'  1744 ;  Shaw's  '  Philosophical  Works  of  Boyle,'  1725. 


CH.  XVII.        FIRST  USE   OF  THE  MICROSCOPE.  137 


CHAPTER   XVII. 

SCIENCE   OF   THE    SEVENTEENTH    CENTURY    (CONTINUED). 

Malpighi  first  uses  the  Microscope  to  examine  Living  Stractures — He 
describes  the  Air-cells  of  the  Lungs — Watches  the  Circulation  of  the 
Blood —Observes  the  Malpighian  layer  in  the  human  Skin — De- 
scribes the  structure  of  the  Silkworm — Leeuwenhoeck  discovers 
Animalcules— Grew  and  Malpighi  discover  the  Cellular  Structure  of 
Plants — The  Stomates  in  Leaves — They  study  the  Germination  of 
Seeds — Ray  and  Willughby  classify  and  describe  Animals  and  Plants 
— The  Friendship  of  these  two  Men. 

Use  of  the  Microscope  by  Malpighi,  1661. — We  have  now 
fairly  left  behind  us  the  first  fifty  years  of  the  seventeenth 
century ;  indeed,  the  experiments  of  Bo3de  and  Mayow  were 
all  made  after  1650.  But  I  wish  especially  here  to  remind 
you  that  we  have  just  begun  the  second  half  of  the  century, 
because  it  will  help  you  to  remember  an  important  study 
which  began  very  quietly  about  this  time,  but  which  has  in 
the  end  opened  out  to  us  an  entirely  new  world  of  discovery. 
In  the  year  1609,  at  the  beginning  of  the  century,  Galileo 
brought  distant  worlds  into  view  by  the  use  of  the  telescope; 
and  in  like  manner  in  the  year  1661,  or  about  the  middle  of 
the  century,  Malpighi,  by  the  use  oi  ^^  microscope^  revealed 
the  wonders  of  infinitely  minute  structures,  or  parts  of  living 
bodies  ;  enabling  men  to  see  fibres,  vessels,  and  germs,  which 
were  as  much  hidden  before  by  their  minuteness  as  the 
moons  of  Jupiter  had  been  by  their  distance.  It  is  not  quite 
certain  who  invented  the  microscope  (fUKpog,  little ;  aKOTriw,  I 
look) ;  but  as  the  first  which  were  made  were  only  telescopes 


138  SEVENTEENTH  CENTURY.  pt.  ni. 

(see  p.  97),  with  lenses  of  such  a  focus  as  to  look  at  an  object 
near  instead  of  far  off,  anyone  may  easily  have  hit  upon  the 
idea.  The  important  point  was  the  use  made  of  them,  and 
this,  as  far  as  regards  the  structure  of  living  beings,  we 
owe  to  Malpighi. 

Marcello  Malpighi  was  born  at  Crevalcuore,  near 
Bologna,  in  the  year  1628 ;  he  became  Professor  of  Medi- 
cine at  the  University  of  Bologna  in  1656,  and  was  early 
distinguished  for  his  discoveries  in  Anatomy,  made  chiefly 
by  the  use  of  the  microscope.  It  is  not  possible  for  us, 
without  a  knowledge  of  anatomy,  to  understand  thoroughly 
the  structures  which  he  described,  but  we  may  be  able  to 
form  a  general  idea  of  the  work  he  did. 

One  of  his  first  experiments  was  the  examination  of  the 
general  circulation  of  the  blood  in  the  stomach  of  a  frog, 
and  he  succeeded  in  demonstrating  the  fact  that  the  arteries 
are  connected  with  the  veins  by  means  of  minute  tubes 
called  capillaries,  thus  proving  beyond  doubt  the  truth  of 
Harvey's  doctrine.  His  next  work  was  to  study  the  passage 
of  the  blood  through  the  lungs  (see  p.  113),  and  to  describe 
the  air-cells  from  which  the  blood  derives  its  oxygen.  If 
you  can  get  anyone  to  show  you  properly  under  the  micro- 
scope a  section  of  a  frog's  lung,  you  will  see  a  number  of 
round  spaces  bordered  by  a  delicate  partition  ;  these  are 
sections  of  air-cells,  and  round  them  you  will  see  a  network 
of  minute  tubes.  Through  these  tubes  or  capillaries  the 
blood  flows  in  a  living  creature,  and  takes  up  oxygen  from 
the  air  through  the  coverings  or  membranes  of  the  air- 
cells  and  capillaries,  giving  back  in  exchange  carbonic  acid 
to  be  breathed  out  into  the  atmosphere.  Malpighi  was  the 
first  to  point  out  these  air-cells  and  to  describe  the  way  in 
which  the  blood  passes  over  them.    After  this  he  turned  his 


CH.  XVII.     IMPORTANT  MICROSCOPIC  DISCOVERIES.     139 


attention  to  th-j  tongue,  and  published  in  1665  a  careful  de- 
scription of  all  its  nerves,  vessels,  and  coverings.  He  also 
pointed  out  that  the  outside  layer  of  the  skin  or  epidermis 
of  the  negro  is  as  white  as  yours  or  mine,  and  that  the 
colouring  matter  which  gives  him  his  dark  colour  is  con- 
tained in  a  deeper  layer  just  at  the  point  where  the  epidermis 
joins  the  dermis  or  real  fibrous  skin  beneath  (see  Fig  21.) 
This  soft  layer  is  still  called 
the  '  Malpighian  layer,'  and 
the  different  colours  of  the 
skins  of  animals  are  caused 
by  little  cells  of  colouring 
matter  which  lie  buried  in  it. 

After  Malpighi  had  ex- 
amined many  other  minute 
structures  of  the  human  body, 
he  began  next  to  study  insects, 
and  in  1669  he  published  a 
beautiful  description  of  the  silkworm. 


Section  of  the  Skin  (Huxley). 

a,  Epidermis,  b,  Its  deeper  layer,  or 
Malpighian  layer,  c,  Upper  part  of 
the  dermis,  or  true  skin,  d  d,  Per- 
spiration ducts. 


With  his  microscope 
he  discovered  the  small  holes  or  pores  which  are  to  be  seen 
along  both  sides  of  the  body  of  insects,  and  he  found  that 
these  pores  were  openings  into  minute  air-tubes,  which  pass 
into  every  part  of  the  insect's  body,  and  form  a  breathing 
apparatus.  He  also  described  the  peculiar  vessels  in  which 
the  silkworm  secretes  the  juice  from  which  its  silk  is  made, 
and  he  traced  the  changes  which  the  different  parts  of  the 
worm  undergo  as  it  turns  into  the  moth.  In  fact,  he  was 
the  first  man  who  attempted  to  trace  out  the  anatomy  of 
such  small  creatures  as  insects  ;  a  study  to  which  men  now 
often  devote  their  whole  lives. 

But  grand  as  Malpighi's  discoveries  were,  a  Dutchman 
named  Leeuwenhceck  (born  1632, died  1723)  made  the  micro- 


I40  SEVENTEENTH  CENTURY.  pt.  hi. 

scope  tell  even  a  more  wonderful  tale,  for  he  detected  in 
water  and  in  the  insides  of  animals  those  extremely  minute 
beings  which  he  called  animalcules.  He  showed  that  a 
piece  of  the  soft  roe  of  the  cod-fish  not  bigger  than  an  ordi- 
nary grain  of  sand  might  contain  ten  thousand oi  these  living 
creatures.  When  such  tiny  beings  as  these  could  be  seen 
and  examined,  I  think  you  will  acknowledge  that  I  did  not 
speak  too  strongly  when  I  said  that  the  microscope  has 
opened  out  to  us  a  new  and  marvellous  world  of  life. 

Vegetable    Anatomy,   Grew    and   MalpigM,   1670. — 
From  insects  IMalpighi   next  turned   to  plants  j   and   it  is 
curious  that  at  about  the  same  time  an  English  botanist 
named  Nehemiah  Grew  (born  1628,  died  171 1),  who  was  se- 
cretary to  the  Royal  Society,  also  took  up  the  same  study  ; 
and  the  papers  of  the  two  men  were  laid  before  the  Royal 
Society  on   the   same  day  in   1670.     Malpighi's  complete 
work  was  afterwards  published  in  1674,  and  Grew's  in  1682. 
The  investigations  of  these  two  men  agreed  in  many  re- 
markable points  ;  they  had  both  of  them  examined  with 
great  care  the  flesh  (if  we  may  call  it  so)  of  plants,  and  they 
described  for  the  first  time  the  tiny  bags  or  cells  of  which 
every  part  of  a  plant  is  made,  and  which  you  may  easily  see 
for  yourself  if  you  put  a  very  thin  piece 
of  the  pulpy  part  of  an  apple,  or  better 
still,    of  the  pith  of  elder   under   the 
microscope  (see  Fig.   22).     They  had 
also  noticed  the  long  tubes  which  He 
among  the  woody  fibres  in  the  stringy 
or  fibrous  part  of  a  plant  and  in  the 
Cellular  tissue  from  the      vcins   of  the  Icavcs,   and    Grew    had 

pith  of  the  elder  (Oliver).  ^ 

pointed    out    quite    truly    that    these 
tubes,  which  are   called  vessels  or  ducts^  are  composed  of 


cii.  XVII.  VEGETABLE  ANATOMY.  141 

Strings  of  cells  which  have  grown  together  into  one  long  cell 
or  tube. 

Grew  also  first  saw  those  beautifiil  little  months  in  the 
skin  of  the  leaves  called  stomates,  which  open  when  the  air 
is  damp,  and  serve  for  taking  in  and  giving  out  air  and 
moisture.     To  see  these  you  must  take  a  very  thin  piece  of 
the  skin  of  the  under  part  of  a  leaf,  and  place  it  in  water 
under  the  microscope  ;  you  will  see  a  number  of  very  small 
roundish  or  oval  spaces  {a,  Fig.  23),  and  if  you  watch  care- 
fully you  will  most  likely  see  some  of  fig.  23. 
them   open  in   the  water.     Grew   dis-  a- 
covered  these  stomates  and  pointed  out           rCt^s^ 
their  use.     He  also  studied  very  care-       D-ViVa?'''^ 
fully  the  way  in  which  seeds  begin  to           v-V^feJs 
sprout ;  but  on  this  point  Malpighi  did             Vn^Ciy 
the   most,  for  he   watched   under  the              ^<-v' 
microscope  the  whole  process  of  the  ^^^^^ken  w  ?h?unde!-- 
growth  of  seeds,  and  described  all  the       f^  liZtTX  CeUs 
different  states  of  the  germ,  comparing       "^  '^^  '^^"  (Carpenter). 
them  to  the  growth  of  a  chicken  in  the  Qgg,  and  showing 
how  much  an  egg  and  a  seed  resemble  each  other  in  many 
particulars. 

By  these  few  examples  you  can  form  an  idea  how  much 
Grew  and  Malpighi  did  towards  the  study  of  the  structure 
of  plants  or  Vegetable  Anatomy,  a  science  which  they  may 
almost  be  said  to  have  founded,  and  one  which  you  may 
work  at  yourself  with  the  help  of  a  fairly  good  microscope 
and  an  elementary  book  on  Botany.  If  you  will  do  this 
with  patience  and  care  you  will  be  well  repaid;  for  some  of 
the  most  beautiful  and  delicate  of  the  contrivances  of  Nature 
lie  hid  in  those  frail  flowers  which  we  gather  for  their 
scent  and  beauty,  and  fling  away  without  imagining  what 


142  SEVENTEENTH  CENTURY.  pt.  hi. 

wonderful  structures  they  can  reveal  to  us  even  when  dead 
and  withered. 

Classification  of  Plants  and  Animals  by  Eay  and 
Willughby,  1693-1705. — We  now  come  to  the  history  of 
two  friends,  which  is  in  itself  a  pleasure  to  dwell  upon, 
even  if  they  had  not  both  been  great  men ;  but  which  be- 
comes much  more  interesting  when  we  remember  that  it  was 
their  love  of  the  study  of  Nature  which  first  brought  them 
together,  and  which  made  them  inseparable,  not  only  in  life, 
but  in  their  works  after  death. 

John  Ray,  one  of  the  greatest  botanists  of  the  seven- 
teenth century,  was  born  near  Braintree,  in  Essex,  in  the 
year  1628.  Though  only  the  son  of  a  blacksmith,  he  re- 
ceived a  good  education  at  the  grammar  school  of  the  town, 
and  went  afterwards  to  Cambridge,  where  he  remained  as  a 
tutor  after  he  had  taken  his  degree.  Here  one  of  his  first 
pupils  was  a  Mr.  Francis  Willughby,  of  Middleton  Hall,  in 
Warwickshire,  a  man  seven  years  younger  than  himself,  and 
belonging  to  quite  a  different  rank  in  society.  These  two 
men,  however,  had  one  great  interest  in  common — they  were 
both  passionately  fond  of  Natural  History,  and  spent  all  their 
spare  time  in  studying  it  together. 

They  soon  found  that  the  descriptions  and  classifications 
of  plants  and  animals  which  had  been  drawn  up  by  earlier 
naturalists  were  very  imperfect,  and  they  formed  the  project 
of  drawing  up  a  complete  classification  of  all  known  plants 
and  animals,  describing  them  as  far  as  they  were  able,  and 
arranging  them  in  groups  according  to  their  different  cha- 
racters. Willughby  undertook  the  birds,  beasts,  and  fishes, 
while  Ray  devoted  himself  chiefly  to  plants;  but  they  worked 
together  in  all  the  branches,  and  Ray,  as  we  shall  see,  ended 
by  doing  far  more  than  his  share  of  the  work. 


CH.  XVII.  ZOOLOGY.  143 

From  1663  to  1666  the  two  friends  travelled  together 
over  England,  France,  Germany,  and  Italy,  making  col- 
lections of  animals  and  plants,  and  Willughby  took  a  pleasure 
in  using  his  wealth  to  add  to  the  knowledge  of  his  poorer 
companion.  Soon  after  their  return  Ray  was  made  a  fellow 
of  the  Royal  Society,  and  Willughby  was  not  long  before  he 
received  the  same  honour.  Willughby  now  married,  and 
though  Ray  continued  his  travels  alone,  yet  a  great  part  of 
his  time  was  spent  at  Middleton  Hall,  where  the  two  friends 
made  experiments  upon  sap  in  the  trees  and  the  way  it 
flows. 

In  this  way  they  worked  together  till,  in  1672,  Mr. 
Willughby  died  of  a  fever,  leaving  a  sum  of  sixty  pounds  a 
year  to  Ray,  and  begging  him  to  bring  up  his  two  little  sons 
and  to  continue  his  works  on  Zoology,  which  he  had  left  un- 
finished. The  way  in  which  Ray  fulfilled  these  requests  fully 
showed  the  affection  which  he  felt  for  his  lost  friend.  He 
brought  up  the  boys  till  they  were  removed  from  his  care  by 
relations  ;  and  as  to  the  works,  he  edited  them  with  so  much 
care  and  such  a  touching  desire  to  give  every  credit  to 
Willughby,  that  much  of  the  work  which  must  have  been 
Ray's  stands  in  his  friend's  name,  and  in  fame,  as  in  life,  it 
is  impossible  to  separate  them. 

I  can  only  give  you  a  very  general  idea  of  the  kind  of 
classifications  which  Ray  and  Willughby  adopted,  for  a  mere 
list  of  classes  would  be  neither  interesting  nor  useful  to  you. 
The  first  book,  which  was  on  Quadrtipeds,  was  published  by 
Ray  in  1693.  He  divided  these  first,  as  Aristotle  had  done, 
into  oviparous,  or  those  that  are  born  from  eggs,  like  frogs 
and  lizards  ;  and  viviparous,  or  those  which  are  bom  alive, 
like  lambs  and  kittens.  He  then  divided  the  viviparous 
quadrupeds  into  those  which  have  the  hoof  all  in  one  piece, 


144  SEVENTEENTH  CENTURY.  pt.  III. 

like  the  horse,  and  those  with  a  spHt  hoof,  Hke  the  ox  and 
goat.  Those  with  spUt  hoofs  he  divided  again  according  as 
they  chewed  the  cud,  Hke  the  ox,  or  did  not,  Hke  the  pig. 
Then  came  the  animals  whose  hoofs  are  split  into  many  parts, 
as  the  hippopotamus  and  rhinoceros  ;  then  those  which  have 
nails  only  in  place  of  toes,  as  the  elephant ;  then  those  which 
have  toes  but  no  separation  between  the  fourth  and  fifth  toes, 
as  the  cat,  dog,  and  mole ;  and  lastly,  those  which  havei  the 
fifth  finger,  or  toe,  quite  separate,  as  the  monkeys.  After 
this  he  divided  them  more  fully,  by  their  teeth,  and  thus 
made  a  very  fair  classification  of  quadrupeds. 

The  book  upon  Birds,  which  comes  next  in  order,  had 
already  been  published  by  Ray  in  1677,  four  years  after 
Willughby's  death.  In  it  birds  were  divided  first  into  land- 
birds  and  water-birds,  and  then  were  classified  by  the  shape 
of  their  beak  and  claws,  and  according  as  they  fed  upon  flesh 
like  the  vulture,  or  upon  fruit  and  seeds  like  the  parrot.  The 
water-birds  were  also  divided  into  those  which  were  long- 
legged,  as  the  flamingo,  or  short-legged,  as  the  duck,  and 
according  as  the  web  between  their  toes  was  more  or  less 
complete. 

The  '  History  of  Fishes '  is  given  as  the  joint  work  of  Ray 
and  Willughby ;  the  groups  into  which  they  divided  them 
are  nearly  the  same  as  those  now  used,  but  they  are  too 
diflicult  to  explain  here. 

The  ^  History  of  Insects  '  was  Ray's  work,  and  was  pub- 
lished by  friends  after  his  death,  in  the  same  way  as  he  had 
published  Willughby's.  He  divided  insects  into — first,  those 
which  undergo  metamorphosis  (that  is,  turn  from  the  cater- 
pillar into  the  moth),  as  the  silkworm,  and  all  moths  and  but- 
terflies ;  and  second,  those  which  do  not  change  their  form ; 
and  then  he  sub-divided  them  according  to  the  number  of 
their  feet,  the  shape  of  their  wings,  and  many  other  characters. 


CH.  XVII.       J^AVS   CLASSIFICATION  OF  PLANTS.  145 

But  Ray's  greatest  work  was  upon  Plants,  which  he 
classified  much  more  perfectly  than  Csesalpinus  had  done. 
He  divided  them  first  into  imperfect  plants^  or  those  whose 
flowers  are  invisible,  as  mosses  and  mushrooms ;  and  pei-fect 
plants^  or  those  having  visible  flowers.  The  perfect  plants 
he  divided  into  two  classes — first,  the  dicotyledons.,  or  those 
whose  seeds  open  out  into  two  seed-leaves,  like  the  wall- 
flower or  the  bean,  in  which  last  you  can  see  the  two  cotyle- 
dons very  clearly  if  you  take  off"  the  outer  skin ;  and  secondly, 
the  monocotyledons,  or  those  whose  seeds  have  only  07ie  large 
seed-leaf,  like  a  grain  of  wheat.  The  dicotyledons  he  again 
divided  into  those  having  simple  flowers,  like  the  buttercup, 
and  those  whose  flowers  are  compound.,  like  the  daisy  j  for  if 
you  pick  a  daisy  to  pieces  you  will  find  that  the  centre  is 
made  up  of  a  number  of  little  flowers,  each  of  them  perfect 
in  itself.  It  will  have  its  own  green  calyx  and  coloured 
corolla,  and  its  o^vn  stamens  and  seed-vessel ;  therefore  each 
daisy  is  a  branch  of  little  flowerets,  or  a  compound  ?iow&[:. 
Ray  went  on  next  to  class  the  simple  flowers  according  to 
the  number  of  seeds  they  bore,  and  the  way  in  which  the 
seeds  were  arranged  in  the  seed-vessel.  In  this  way  he 
made  a  rough  but  complete  classification  of  all  the  known 
plants.  Linnsus,  the  great  botanist  of  the  eighteenth 
century,  adopted  many  of  Ray's  divisions,  which  had  mean- 
while been  made  more  perfect  by  Joseph  Toumefort,  a 
Frenchman,  bom  at  Aix,  in  Provence,  in  1656. 

Ray  outlived  his  friend  Willughby  more  than  thirty 
years,  and  died  in  1705  at  the  age  of  seventy-seven.  His 
death  brings  us  to  the  end  of  the  Natural  History  of  the  seven- 
teenth century,  so  far  as  we  have  been  able  to  notice  it.  But 
I  cannot  too  often  remind  you  that  these  four  men,  Malpighi, 
Grew,  Ray,  and  Willughby,  are  merely  a  few  among  an 
8 


146  SEVENTEENTH  CENTURY.  pt.  hi. 

immense  number  of  observers  in  the  same  line  of  study.  I 
have  picked  out  those  whose  work  you  could  best  under- 
stand, and  whose  names  ought  to  be  known  to  you  ;  but  I 
could  have  selected  not  four  but  forty  others  who  ought  to 
have  been  mentioned,  if  my  book  and  your  knowledge  had 
been  greater.  We  must  be  content  to  catch  here  and  there  a 
glimpse  of  the  advance  that  was  being  made,  always  remem- 
bering that  an  almost  inexhaustible  store  of  further  infor- 
mation remains  behind  when  we  have  opportunity  to  seek 
for  it. 

Chief  Works  consulted. — Cuvier,  'Hist,  des  Sciences  Naturelles  ; ' 
Carpenter's  '  Physiology  ; '  Sprengel,  '  Histoire  de  la  Medecine  ; ' 
Whewell's  '  History  of  Inductive  Sciences  ; '  Carpenter,  '  On  the  Micro- 
scope ; '  '  Memorial  of  John  Ray,'  E.  Lankester,  1846  ;  *  Life  of  Ray 
and  Willughby,'  Naturalists'  Library,  vol.  xxxv.  ;  Lardner's  *  Encyclo- 
paedia '—Classification  of  Animals. 


cii.  XVIII.  SIR  ISAAC  NEWTON.  147 


CHAPTER   XVIII. 

SCIENCE   OF   THE    SEVENTEENTH    CENTURY    (CONTINUED). 

1642,  Birth  of  Newton — His  Education — 1666,  His  three  great  Dis- 
coveries first  occur  to  him — Method  of  Fluxions  and  Differential 
Calculus — First  thought  of  the  Theory  of  Gravitation — Failure  of 
his  Results  in  consequence  of  the  Faulty  Measurement  of  the  size  of 
the  Earth — 1682,  Hears  of  Picart's  new  Measurement — Works  out 
the  result  correctly,  and  proves  the  Theory  of  Gravitation — Ex- 
planation of  this  Theory — Establishes  the  Law  that  Attraction 
varies  inversely  as  the  squares  of  the  distance — 1687,  Publishes  the 
'  Principia ' — Some  of  the  Problems  dealt  with  in  this  Work. 

Newton,  1642. — We  must  now  leave  the  living  creation  to 
return  to  physical  science,  for,  during  all  those  years  with 
which  we  have  been  occupied  since  the  time  of  Galileo 
and  Kepler,  a  boy  had  been  growing  up  into  rcanhood,  who 
was  to  become  one  of  the  greatest  men  of  science  that  Eng- 
land has  ever  known.  In  1642,  the  same  year  in  which 
Galileo  died,  a  child  was  bom  at  Woolsthorpe,  near  Gran- 
tham in  Lincolnshire,  who  was  so  tiny  that  his  mother  said 
^  she  could  put  him  into  a  quart  mug.'  This  tiny  delicate 
baby  was  to  become  the  great  philosopher  Newton. 

We  hear  of  him  that  he  was  at  first  very  idle  and  inattentive 
at  school,  but,  having  been  one  day  passed  in  the  class  by 
one  of  his  schoolfellows,  he  determined  to  regain  his  place, 
and  soon  succeeded  in  rising  to  the  head  of  them  all.  In 
his  play  hours,  when  the  other  boys  were  romping,  he 
amused  himself  by  making  little  mechanical  toys,  such  as  a 


148  SEVENTEENTH  CENTURY.  pt.  hi. 

water  clock,  a  mill,  turned  by  a  mouse,  a  carriage  moved 
by  the  person  who  sat  in  it,  and  many  other  ingenious  contri- 
vances. When  he  was  fifteen  his  mother  sent  for  him  home 
to  manage  the  farm  which  belonged  to  their  estate  \  but  it 
was  soon  clear  that  he  was  of  no  use  as  a  farmer,  for  though 
he  tried  hard  to  do  his  work,  his  mind  was  not  in  it,  and  he 
was  only  happy  when  he  could  settle  down  under  a  hedge 
with  his  book  to  study  some  difficult  problem.  At  last  one 
of  his  uncles,  seeing  how  bent  the  boy  was  upon  study,  per- 
suaded his  mother  to  send  him  back  to  school  and  to 
college,  where  he  soon  passed  all  his  companions  in  mathe- 
matics, and  became  a  Fellow  of  Trinity  College,  Cambridge, 
in  1667.  But  even  before  this,  in  the  year  1666,  his  busy 
mind  had  already  begun  to  work  out  the  three  greatest  dis- 
coveries of  his  life.  In  that  year  he  invented  the  remarkable 
mathematical  process  called  the  ^  Method  of  Fluxions^  \f\i\Qh 
is  almost  the  same  as  that  now  called  the  'Differential 
Calculus,'  invented  about  the  same  time  by  Leibnitz,  a  great 
German  mathematician.  In  that  year  he  also  made  the  dis- 
coveries about  Light  and  Colour ^  which  we  shall  speak  of 
by-and-by  ;  and  again  in  that  year  he  first  thought  out  the 
great  Theory  of  Gravitation^  which  we  must  now  consider. 

Theory  of  Gravitation,  1666. — In  the  course  of  his 
astronomical  studies,  Newton  had  come  across  a  problem 
which  he  could  not  solve.  The  problem  was  this.  Why 
does  the  moon  always  move  round  the  earth,  and  the  planets 
round  the  su;i?  The  natural  thing  is  for  a  body  to  go 
straight  on.  If  you  roll  a  marble  along  the  floor  it  moves 
on  in  a  straight  line,  and  if  it  were  not  stopped  by  the  air 
and  the  floor,  it  would  roll  on  for  ever.  Why,  then,  should  the 
bodies  in  the  sky  go  round  and  round,  and  not  straight  fo7"ward  1 

While  Newton  was  still  pondering  over  this  question,  the 


CH.  xvni.  NEWTON S  STUDIES.  149 

plague  broke  out  in  Cambridge  in  the  year  1665,  and  he  was 
forced  to  go  back  to  Woolsthorpe.  Here  he  was  sitting  one 
day  in  the  garden,  meditating  as  usual,  when  an  apple  from 
the  tree  before  him  snapped  from  its  stalk  and  fell  to  the 
ground.  This  attracted  Newton's  attention  ;  he  asked 
himself,  Why  does  the  apple  fall  ?  and  the  answer  he  found 
was,  Because  the  earth  pulls  it.  This  was  not  quite  a  new 
thought,  for  many  clever  men  before  Newton  had  imagined 
that  things  were  held  down  to  the  earth  by  a  kind  of  force, 
but  they  had  never  made  any  use  of  the  idea.  Newton,  on 
the  contrary,  seized  upon  it  at  once,  and  began  to  reason 
farther.  If  the  earth  pulls  the  apple,  said  he,  and  not  only 
the  apple  but  things  very  high  up  in  the  air,  why  should  it 
not  pull  the  moon,  and  so  keep  it  going  round  and  round 
the  earth  instead  of  moving  on  in  a  straight  line  ?  And  if 
the  earth  pulls  the  moon,  may  not  the  sun  in  the  same  way 
pull  the  earth  and  the  planets,  and  so  keep  them  going 
round  and  round  with  the  sun  as  their  centre,  just  as  if  they 
were  all  held  to  it  by  invisible  strings  ? 

You  can  understand  this  idea  of  Newton's  by  taking  a 
ball  with  a  piece  of  string  fastened  to  it,  and  swinging  it 
round.  If  you  were  to  let  the  string  go,  the  ball  would  fly 
off  in  a  straight  line,  but  as  long  as  you  hold  it,  it  will  go 
round  and  round  you.  Thus  Newton  imagined  that  every- 
thing near  the  earth  is  pulled  towards  it  by  an  invisible  force, 
as  you  would  pull  the  ball  by  the  string  \  but  the  ball  does 
not  come  to  you,  although  the  string  pulls  it,  because  of  the 
other  force  which  is  carrying  it  onwards  j  and  in  the  same, 
way  the  moon  would  not  come  to  the  earth,  but  would  go  on 
revolving  round  it. 

Newton  felt  convinced  that  this  guess  was  right,  and  that 
\kiQ  force  of  gravitation,  as  he  called  it,  kept  the  moon  going 


I50  SEVENTEENTH  CENTURY.  ft.  hi. 

round  the  earth,  and  the  planets  round  the  sun.  But  a  mere 
guess  is  not  enough  in  science,  so  he  set  to  work  to  prove  by 
very  difficult  calculations  what  the  effect  ought  to  be  if  it  was 
true  that  the  earth  pulled  or  attracted  the  moon.  To  make 
these  calculations  it  was  necessary  to  know  exactly  the 
distance  from  the  centre  of  the  earth  to  its  surface,  because 
the  attraction  would  have  to  be  reckoned  as  strongest  at  the 
centre  of  the  earth,  and  then  as  gradually  decreasing  till  it 
reached  the  moon.  Now  the  size  of  the  earth  was  not  accu- 
rately known,  so  Newton  had  to  use  the  best  measurement 
he  could  get,  and  to  his  great  disappointment  his  calcula- 
tions came  out  wrong.  The  moon  in  fact  moved  more 
slowly  than  it  ought  to  do  according  to  his  theory.  The 
difference  was  small,  for  the  pull  of  the  earth  was  only  one- 
sixth  greater  than  it  should  have  been  :  but  Newton  was  too 
cautious  to  neglect  this  error.  He  still  believed  his  theory 
to  be  true,  but  he  had  no  right  to  assume  that  it  was,  unless 
he  could  work  it  out  correctly.  So  he  put  away  his  papers 
in  a  drawer  and  waited  till  he  should  find  some  way  out  of 
the  difficulty. 

This  is  one  of  many  examples  of  the  patience  men  must 
have  who  wish  to  make  really  great  discoveries.  Newton 
waited  sixteen  years  before  he  solved  the  problem,  or  spoke 
to  anyone  of  the  great  thought  in  his  mind.  But  more 
light  came  at  last ;  it  was  in  1666,  when  he  was  only  twenty- 
four,  that  he  saw  the  apple  fall ;  and  it  was  in  1682  that  he 
heard  one  day  at  the  Royal  Society  that  a  Frenchman 
named  Picart  had  measured  the  size  of  the  earth  very  accu- 
rately, and  had  found  that  it  was  larger  than  had  been  sup- 
posed. Newton  saw  at  once  that  this  would  alter  all  his 
calculations.  Directly  he  heard  it  he  went  home,  took 
out  his  papers,  and  set  to  work  again  with  the  new  figures. 


en.  XVIII.  THE  LAW  OF  GRAVITATION.  151 

Imagine  his  satisfaction  when  it  came  out  perfectly  right ! 
It  is  said  that  he  was  so  agitated  when  he  saw  that  it  was 
going  to  succeed,  that  he  was  obHged  to  ask  a  friend  to 
finish  working  out  the  calculation  for  him.  His  patience  was 
rewarded  \  the  attraction  of  the  earth  exactly  agreed  with  the 
rate  of  movement  of  the  moon,  and  he  knew  now  that  he 
had  discovered  the  law  which  governed  the  motions  of  the 
heavenly  bodies. 

This  law  of  Newton's  is  called  the  *  Law  of  Gravttatmi,^ 
and  we  must  now  try  to  understand  what  it  is.  Gravitation 
means  the  drawing  of  one  thing  towards  another,  or  towards 
a  centre.  All  the  objects  upon  our  earth  are  held  there  by 
gravity,  which  pulls  or  attracts  them  towards  the  centre  of 
the  earth.  If  there  were  no  such  thing  as  gravity  there  would 
be  nothing  to  prevent  our  chairs  and  tables,  and  even  our- 
selves, from  flying  into  space ;  but  they  are  all  held  to  the 
earth  by  gravity,  and  if  you  dig  a  hole  under  them  they 
fall  directly  nearer  to  the  centre. 

Now  let  us  see  how  this  attraction  of  gravitation  affects 
the  planets.  Every  one  of  the  bodies  in  the  heavens  pulls  or 
attracts  all  the  other  bodies,  just  in  the  same  way  as  the  earth 
attracts  the  apple  on  the  tree.  But  as  they  are  all  moving 
rapidly  along  (like  the  ball  swung  round  your  head)  they  do 
not  fall  into  each  other,  but  the  smaller  bodies  move  round 
the  larger  ones  which  are  near  them,  just  as  if  they  were 
fastened  to  them  by  invisible  elastic  threads.  The  smaller 
ones  move  round  the  larger  one,  because  it  is  not  only 
each  body  as  a  whole  which  pulls  the  other  bodies,  but 
every  tiny  atom  of  matter  in  each  planet  is  pulling  at  all 
the  atoms  in  all  the  other  planets;  so  that  the  bigger  a 
body  is,  and  the  more  atoms  it  has  in  it,  the  more  it  will 
draw  other  bodies  towards  it.     Our  sun  pulls  the  planets, 


152 


SEVENTEENTH  CENTURY. 


PT.  III. 


and  the  planets  pull  the  sun ;  but  our  sun  has  700  times 
more  atoms  in  it  than  all  the  planets  put  together,  and  so  it 
keeps  them  moving  round  it.  In  the  same  way  our  earth 
has  eighty  times  more  atoms  in  it  than  our  moon,  and  so  it 
keeps  the  moon  moving  round  it. 

In  this  way  the  force  of  gravity  keeps  all  the  different 
planets  in  their  paths  or  orbits.  It  does  not  set  them  moving  ; 
some  other  force  unknown  to  us  first  started  them  across  the 
sky — gravitation  is  only  the  force  which  determines  the  direc- 
tion in  which  they  move. 

It  was  a  grand  thing  to  have  discovered  this  force,  but  it 
would  have  been  of  little  value  to  Astronomy  to  know  that 
the  heavenly  bodies  attracted  each  other  unless  it  could  also 
be  known  how  much  influence  they  have  upon  each  other. 
This  also  Newton  worked  out  accurately.  You  will  remem- 
ber that  Kepler  had  shown  that  planets  move  in  ellipses, 
having  the  sun  in  one  of  the  two  foci  (see  fig.  10,  p.  99). 
Knowing  this,  Newton  was  able  to  calculate  how  much  the 
sun  attracts  a  planet  when  it  is  near,  and  how  much  when  it 
is  far  off,  so  as  to  make  it  move  in  an  ellipse  j  and  he  found 

that  exactly  as  much  as  the 
square  of  the  distance  increases, 
so  much  the  attraction  de- 
creases ;  that  is,  the  attraction 
grows  less  and  less  at  a  regular 
rate  as  you  go  farther  away 
from  the  body  that  is  pulling. 
For  instance,  suppose  that 
at  the  point  i,  fig.  24,  a  planet 
was  one  million  of  miles  away 
from  the  sun,  and  was  being 
When  it  arrived  at  the  point 


attracted  with  immense  force. 


CH.  XVIII.  THE    '  FRINCIPIA: 


153 


3  it  would  be  about  twice  as  far,  or  two  millions  of  miles 
distant ;  and  the  square  of  2  being  4  (2    x  2  =  4),  the  at- 
traction of  the  sun  at  this  point  will  be  only  one-fourth  as 
much  as  it  was  at  the  point  i.     At  the  point  7  the  planet 
would  be  about  three  times  as  far,  or  three  millions  of  miles 
from  the  sun,  and  as  the  square  of  3  is  9  (3  x  3  =  9),  the 
attraction  here  will  be  only  ith  of  the  attraction  at  the  point 
I.     And  so  the  calculation  goes  on ;  if  the  planet  went  12 
millions  of  miles  off,  the  attraction  would  be  y^^  what  it  was 
at  first,  and  at  92  milHons  of  miles  the  attraction  would  be 
¥T6"¥  5  so  that  when  the  planet  is  very  far  away  the  attraction 
becomes  very  slight  indeed,  but  it  will  never  entirely  cease. 
In  scientific  language  this  law  is  expressed  by  the  words, 
The  attractioit  vai'ies  inversely  as  the  square  of  the  distance. 
When  once   this  law  was  known,  it  explained   in   a  most 
beautiful  and  complete  way  not  only  the  three  laws  of  Kep- 
ler, but  all  the  complex  movements  of  the  heavenly  bodies. 
These  Newton  worked  out  with  the  greatest  accuracy  by 
the  help  of  his  '  Method  of  Fluxions,'  which  enabled  him 
to  calculate  all  the  varying  rates  at  which  the  planets  move 
in  consequence  of  their  mutual  attraction ;  and  he  showed 
that  whenever  we  know  clearly  the  position  and  mass  of  all 
the  bodies  attracting  a  planet,  the  law  of  gravitation  exactly 
accounts  for  the  direction  in  which  it  moves. 

If  you  will  consider  for  a  moment  what  a  labour  it  must- 
be  to  calculate  how  much  all  the  different  planets  pull  each 
other  at  different  times — when  they  are  near  together  and 
when  they  are  far  off,  when  they  are  near  each  other  and 
near  th  sun,  or  near  each  other  and  far  from  the  sun,  in 
fact  in  all  the  different  positions  you  can  imagine — you  may 
form  some  idea  of  the  tremendous  work  he  did.  When  he 
published  his  great  book,  the  '  Principia,'  in  1687,  there  were 


154  SEVENTEENTH  CENTURY.  pt.  III. 

iiot  more  than  eight  people  in  the  world  who  were  able  to 
understand  the  full  meaning  of  his  calculations  and  reason- 
ings; and  though  his  theory  of  gravitation  was  well  received, 
and  his  name  became  one  of  the  most  renowned  and 
honoured  in  the  world,  yet  it  was  more  than  fifty  years 
before  his  work  was  thoroughly  appreciated. 

It  may  therefore  easily  be  imagined  that  it  is  not  possible 
to  give  a  simple  sketch  of  what  is  contained  in  the  '  Prin- 
cipia ; '  but  some  idea  may  perhaps  be  formed  of  the 
grandeur  of  the  law  of  gravitation  from  an  enumeration  of 
some  of  the  problems  which  Newton  explained  by  its  action. 

1.  He  explained  those  laws  of  motion  which  Galileo  had 
proved  by  experiment,  and  showed  that  it  is  the  force  of 
gravity  which  causes  the  weight  of  bodies ;  and  determines, 
when  combined  with  other  laws,  the  rate  at  which  they  fall, 
and  the  path  they  describe. 

2.  He  worked  out  the  specific  gravity  of  the  planets, 
showing,  for  example,  that  the  matter  of  which  Saturn  is 
composed  is  about  nine  times  lighter  than  the  matter  of  our 
earth. 

3.  He  showed  how  the  attractions  of  the  sun  and  of  the 
moon  cause  the  tides  of  the  sea,  and  worked  out  accurately 
the  reason  of  the  spring  and  neap  tides. 

4.  He  proved  that  the  earth  could  not  be  a  perfect  globe, 
and  measured  almost  exactly  how  great  the  bulge  at  the 
equator  and  the  flattening  at  the  poles  must  be.  And  this 
he  did  entirely  by  calculation,  for  no  measurements  had  then 
been  made,  to  lead  anyone  to  doubt  that  the  earth  was  a 
perfect  globe. 

5.  He  gave  a  complete  explanation  of  the  cause  of  the 
*  precession  of  the  equinoxes,'  the  occurrence  of  which,  as 
you  will  remember,  Hipparchus  had  discovered  (see  p.  30). 


CH.  XVIII.     LAW  OF  GRAVITATfON  EXPLAINED.  155 

6.  He  not  only  showed  why  the  planets  move  in  ellipses 
while  a  line  joining  the  sun  and  a  planet  cuts  off  equal  areas 
in  equal  times;  but  he  also  accounted  for  many  irregularities 
in  these  movements,  arising  from  their  mutual  attractions, 
thus  showing  that  gravitation  exj)lains  not  only  the  general 
laws  but  even  apparent  exceptions. 

7.  Of  all  bodies  comets  are  apparently  the  most  irregu- 
lar, yet  Newton  calculated  that  they  probably  move  in  a 
peculiar  curve  called  a  parabola,  and  since  his  time  it  has 
been  proved  that  the  motions  of  all  comets  can  be  suffi- 
ciently well  explained  by  this  theory,  with  the  exception  of 
a  few  which  move  in  ordinary  ellipses  like  the  planets,  and 
return  periodically.  These  and  many  other  problems  of 
the  universe  Newton  showed  could  all  be  referred  to  the 
action  of  gravitation ;  and  he  concluded  his  work  with  a 
grand  description  of  the  mechanism  of  the  heavens,  dwelling 
with  deep  reverence  upon  the  thought  of  that  Infinite  Mind 
which  gave  rise  to  such  a  wonderful  and  complex  machinery, 
working  in  perfect  order. 


Chief  Works  consulted. — Brewster's  'Life  of  Newton;'  '  Lives  of 
Eminent  Persons ' — Lib.  of  Useful  Knowledge  ;  Airy's  '  Elementary 
Astronomy  ; '  Airy,  '  On  Gravitation.' 


156  SEVENTEENTH  CENTURY.  I'x.  in. 


CHAPTER  XIX. 

SCIENCE    OF   THE    SEVENTEENTH    CENTURY    (CONTINUED). 

Transits  of  Mercuiy  and  Venus — Kepler  foretells  their  occurrence — 
1 63 1,  Gassendi  observes  a  Transit  of  Mercury — 1639,  Horrocks 
foretells  and  observes  a  Transit  of  Venus — 1676,  Halley  sees  a 
Transit  of  Mercury,  and  it  suggests  to  him  a  method  for  Measuring 
the  Distance  of  the  Sun — 1691-1716,  Halley  describes  this  method 
to  the  Royal  Society — Explanation  of  Halley's  method. 

First  transits  ever  observed  of  Mercury  and  Venus,  1631- 
1639. — We  must  now  pause  for  a  moment  before  passing  on 
to  Newton's  discoveries  in  Optics,  in  order  to  mention  a  re- 
markable astronomical  suggestion  made  about  this  time  by 
the  astronomer  Halley  (born  1656,  died  1742),  who  was  the 
friend  and  disciple  of  Newton. 

You  cannot  fail  to  have  heard  and  read  something  about 
the  expeditions  sent  last  Decemberj  1874,  into  all  parts  of 
the  world  to  observe  the  Transit  (or  Passage)  of  Venus 
across  the  sun.  The  object  of  these  observations  was  to 
measure  the  sun's  distance  from  the  earth  j  and  Halley  was 
the  first  to  propose  this  method  of  measurement,  in  1691, 
and  to  show  how  it  might  be  accomplished. 

You  know  that  the  two  planets  Mercury  and  Venus  are 
nearer  to  the  sun  than  our  earth  is,  and  are  therefore  con- 
stantly passing  between  us  and  it.  But  usually  they  pass 
either  below  or  above  the  sun,  and  it  is  only  rarely  that 
they  cross  over  the  bright  disc,  so  as  to  be  seen  through 


CH.  XIX.     THE   TRANSIT  OF   VENUS  FIRST  SEEN.       157 


the  telescope  as  a  round  black  spot  upon  the  sun's  face. 
With  Mercury  this  happens  at  intervals  of  from  seven  to 
thirteen  years  \  but  with  Venus  it  is  much  more  rare,  for 
though  two  transits  generally  come  together  with  an  in- 
terval of  only  eight  years  between  them,  yet  after  this  there 
is  a  gap  of  more  than  a  hundred  years  before  another 
transit  occurs. 

After  Kepler  had  finished  the  famous  Rudolphine  Tables 
he  was  able  to  use  them  to  calculate  when  these  transits 
would  take  place  ;  and  he  showed  that  both  Mercury  and 
Venus  would  cross  the  sun's  disc  on  certain  days  in  the 
year  1631.  A  French  philosopher  named  Gassendi  took 
advantage  of  this  prediction,  and  managed  to  observe  Mer- 
cury passing  across  the  face  of  the  sun  on  November  7, 163 1. 
He  was  the  first  who  ever  observed  a  transit.  With  Venus 
he  was  not  so  fortunate,  for  the  transit  of  that  planet  took 
place  when  it  was  night  at  Paris,  and  so  Gassendi  had  no 
chance  of  observing  it. 

It  was  not  long,  however,  before  this  too  was  seen. 
You  will  remember  that  two  transits  of  Venus  occur  close 
together  with  only  eight  years  between  them.  Now  Kepler 
had  imagined  that  in  1639  Venus  would  pass  a  little  to  the 
south  of  the  sun,  and  so  no  transit  would  take  place.  A 
young  Englishman,  however,  named  Jeremiah  Horrocks, 
only  twenty  years  of  age,  after  going  carefully  over  Kepler's 
tables,  felt  convinced  that  there  would  be  a  transit,  and  he 
even  calculated  within  a  few  minutes  the  time  when  Venus 
would  enter  upon  the  sun's  face.  Full  of  enthusiasm  at  the 
chance  of  seeing  this  grand  sight,  he  wrote  to  a  friend  at  a 
distance,  begging  him  also  to  watch  through  the  telescope  at 
three  o'clock  on  the  afternoon  of  December  4,  1639.  His 
expectations  were  not  disappointed,  for  at  fifteen  minutes 


158  SEVENTEENTH  CENTURY.  pt.  hi. 

past  three  on  that  day  the  planet  began  to  creep  over  the 
face  of  the  sun.  For  twenty  minutes  Horrocks  watched  it, 
and  then  the  sun  set  and  he  could  see  no  more.  He  had 
been  able  to  notice,  however,  that  Venus  was  much  smaller 
in  comparison  with  the  sun  than  had  been  formerly  supposed. 
Horrocks  and  his  friend  Crabtree  were  the  only  people  in 
the  whole  world  who  saw  this  transit  of  Venus,  the  first  one 
ever  observed. 

Halley  suggests  that  the  Sun's  distance  may  be 
measured  by  the  Transit  of  Venus,  1691. — This  was  all 
that  was  known  about  transits  when  Halley  went  to  St. 
Helena  in  1676  to  study  the  stars  of  the  southern  hemi- 
sphere. Here  he  also  observed  a  transit  of  Mercury,  and 
after  watching  the  small  black  spot  travelling  across  the 
face  of  the  sun,  and  noting  the  time  it  took  in  going  from 
one  side  to  the  other,  the  idea  occurred  to  him  that  it 
would  be  possible  to  learn  the  distance  of  the  sun  by  mea- 
suring the  path  of  a  planet  across  its  face.  As  Mercury, 
however,  is  very  fa,r  from  us,  and  near  to  the  sun,  it  would 
not  answer  the  purpose  so  well  as  Venus,  which  is  much 
nearer  the  earth. 

Halley  knew  that  another  transit  of  Venus  would  take 
place  in  1761,  and  as  he  could  not  hope  to  live  till  then,  he 
read  a  paper  to  the  Royal  Society  in  1691,  and  another  in 
1 7 16,  beseeching  the  astronomers  who  should  live  after  him 
not  to  let  such  an  opportunity  pass,  and  describing  the  way 
in  which  the  observations  should  be  made.  It  is  this 
method  which  we  must  now  try  to  understand  as  far  as  it  is 
possible  without  mathematics. 

First  of  all  I  must  tell  you  two  facts  which  astronomers 
knew  already.  The  proportion  of  the  distances  of  the 
planets  was  ascertained,  as  you  will  remember,  by  Kepler 
(see  p.  roo).    Therefore  it  was  known  that  Venus  is  (^w.  round 


CH.  XIX.  H ALLEY'S  METHOD.  159 

numbers)  2\  times  as  far  from  the  sim  as  she  is  from  the 
earth.  It  was  also  known  by  the  apparent  size  of  the  sun 
that  the  sufis  distance  is  about  108  times  his  diameter.,  or,  in 
other  words,  if  you  could  measure  the  number  of  miles 
across  the  face  of  the  sun  and  multiply  that  number  by 
108,  it  would  give  you  the  sun's  distance  from  the  earth. 
Therefore  you  see  the  one  point  to  be  learnt  was.  How 
many  miles  wide  is  the  face  of  the  sun  ? 

Now  suppose  you  place  a  globe  or  any  other  object  upon 
the  table  in  the  middle  of  the  room,  as  at  G,  Fig.  25,  and  place 
yourself  at  the  point  a. 
The  globe  will  then  hide 
from  you  (or  eclipse)  the 
point  c  on  the  opposite 
wall.  Move  your  posi- 
tion to  B,  and  the  globe 
will  then  hide  the  point 
D.  If  the  globe  is  (as 
at    g)    exactly  half-way  ^.  ^    -^ ,       ,    ,■"      t. ,     „  .^.. 

'                    ■'                       ■'  Diagram  showing  how  the  distance  between  the 

between     VOU  and     the  points  p  c  and  d  c  can  be  known,  without 

•'  measuring  them. 

wall       t"hf»    two  nnintS    D  g,  A  globe  half-way  between  d  c  and  a  b.    ^,  A 

and  c  will  be  the  same 

distance  apart  as  the  points  a  and  b.  But  if  you  move  the 
globe  to  g,  which  is  three  tim.es  as  far  from  the  opposite  wall 
as  it  is  from  you,  then  the  points  d  and  c  will  also  be  three 
times  as  far  apart  as  the  points  a  and  b.  So  that  by  know- 
ing how  much  farther  the  globe  is  from  the  wall  than  it  is 
from  you,  you  can  tell  accurately  the  distance  between  the 
points  hidden  without  measuring  them. 

It  is  exactly  in  this  way  that  Halley  proposed  to  measure 
off  a  certain  number  of  miles  upon  the  face  of  the  sun.  We 
are  able  to  learn  accurately  how  many  miles  distant  any  two 
places  are  upon   our  globe.     Suppose,  therefore,  that  two 


i6o  SEVENTEENTH  CENTURY.  ft.  in. 

men  go  to  places  7,200  miles  apart,  and  each  observes  Venus 
at  a  particular  moment  upon  the  sun's  face.  Just  as  you, 
from   two   different   positions,    saw   the    globe   cover    two 

Fig.  26. 


Venus  as  seen  upon  the  sun  by  two  observers,  one  at  e'  and  one  at  E.     (Proctor.) 

s.  The  sun.  V  v',  Appearance  of  Venus  on  the  sun's  face.     Venus  Is  travelling-  in  the 
direction  of  the  arrow. 

different  points  of  the  wall,  so  these  men  will  see  Venus 
against  different  points  in  the  sun,  as  in  Fig.  26  \  and  since  the 
distance  between  Venus  and  the  sun  is  2  J  times  her  distance 
from  the  earth,  the  two  points  will  be  2 J  times  7,200  miles, 
that  is  18,000  miles  apart.  Here,  then,  we  have  a  certain 
number  of  miles  measured  off  on  the  sun's  face.  But  how 
are  we  to  tell  accurately  what  proportion  this  interval  be- 
tween the  spots  bears  to  the  whole  diameter  of  the  sun  ? 

By  Halley's  method  the  whole  time  that  Venus  takes  in 
crossing  the  sun  is  used  as  the  means  of  measurement. 
The  observer  at  each  of  the  two  stations  notes  exactly  the 
time  when  Venus  begins  to  cross  the  face  of  the  sun,  and 
the  moment  when  she  passes  off  it  again,  and  so  reckons 
exactly  how  long  she  has  taken  in  making  the  whole  transit. 

It  was  already  known,  from  the  rate  at  which  Venus 
moves,  exactly  how  long  she  would  take  in  crossing  the 
centre  or  widest  part  of  the  sun.  We  will  call  this  time  6 
hours,  so  as  to  use  whole  numbers.  But  it  is  clear  that  in 
crossing  a  narrower  part  of  the  disc  she  will  take  less  time. 
Suppose,  therefore,  that  one  man  says  she  was  exactly  5 


CH.  XIX.  THE  SUN'S   DIAMETER.  i6i 

hours  crossing  from  a  to  b,  Fig.  27,  and  the  other  that  she 
was  5j  hours  crossing  from  c  to  d.  This  will  give  us  the 
measurement  necessary  to  lay  p^^ 

down  the  position  of  the  two 
transits  on  paper. 

Draw  a  circle  any  size 
you  please,  and,  ruling  a  line 
across  the  centre,  divide  it 
into  six  parts  (as  in  Fig.  27^), 
to  represent  the  6  hours  which 
Venus  would  take  in  crossing 
the  centre ;  each  of  those  parts 
will   then  represent  the   dis-  Transit  of  Venus. 

tance  which  she  travels  in  an  s,  Face  of  the  sun.  v,  Venus.   a  b, 

Transit  observed  so  as  to  occupy  five 
hour  :    5x    of   these,   tlierefore,  hours,     c  d.  Same  transit  observed  so 

as  to  occupy  five-and-a-quarter  hours. 

will  be  the  distance  she  travels 

in  5:^  hours.  Take  this  length  in  your  compasses,  and 
place  it  at  any  part  of  the  circle  where  it  will  meet  the  edge 
at  both  ends,  and  in  that  position  draw  the  line  c  d.  Then 
take  a  second  length  of  five  parts  only,  and  placing  it  below 
the  other,  rule  the  line  a  b  parallel  to  c  d.  These  two 
lines  express  the  path  of  Venus,  as  observed  by  the  two 
men,  and  we  already  know  that  the  distance  between  them 
is  2 J  times  7,200,  or  18,000  miles. 

It  is  now  easy  to  compare  this  interval  with  the  sun's 
diameter.  Suppose  for  instance  that  47  such-  spaces  will 
cover  the  whole  diameter  of  the  circle,  as  they  would  if  the 
lines  were  drawn  accurately  in  the  observed  positions,  then 
18,000  X  47,  or  846,000  miles,  would  be  the  measure  of  the 
sun's  diameter.     Now,  we  saw  (p   159)  that  the  sun's  dis- 

*  It  must  be  drawn  very  much  larger  to  approach  to  anything  like 
accuracy.     This  figure  merely  indicates  the  method. 


iG2  SEVENTEENTH  CENTURY.  pt.  hi. 

tance  is  io8  times  his  diameter ;  therefore  846,000  x  108, 
or  91,368,000  miles  would,  by  these  measurements,  be  the 
distance  of  the  sun  from  the  earth;  and  this  is  as  near  as  we 
can  arrive  at  the  truth  when  taking  whole  numbers. 

You  will  perhaps  ask,  if  the  measurement  of  the  transit  is 
such  a  simple  process,  why  it  takes  months  to  make  the 
proper  calculations.  But  you  must  remember  that  in  our 
description  we  have  neglected  all  the  difficulties  which  really 
occur.  Our  earth  is  not  standing  still  as  we  have  supposed 
it  to  be.  It  is  not  only  moving  along  in  its  orbit,  but  it  is 
turning  round  on  its  axis  all  the  time,  and  this  has  to  be 
very  carefully  considered  in  choosing  stations  for  observing 
the  transit,  and  allowed  for  in  the  results.  Then,  since  our 
earth  moves  in  an  ellipse,  we  are  not  always  at  the  same 
distance  from  the  sun ;  this  also  has  to  be  allowed  for. 
Such  simple  difficulties  as  these  you  can  understand,  but 
there  are  a  great  number  of  others  which  make  the  calcula- 
tions very  complicated  indeed.  Therefore  you  must  not 
imagine  that  you  know  all  about  the  transit  of  Venus  when 
you  have  read  this  description  of  Halley's  method.  If  you 
have  some  general  idea  of  the  way  by  which  the  sun's 
distance  is  found  out,  you  will  have  learnt  more  than  many 
people ;  and  you  must  wait  till  you  have  studied  mathe- 
matics before  you  can  expect  to  have  a  thorough  knowledge 
of  the  matter. 

You  will-  be  glad  to  hear  that  Halley's  advice  was  not 
neglected.  Several  transit  expeditions  were  sent  out  in  1761, 
and  again  in  1769,  when  the  celebrated  Captain  Cook  made  a 
voyage  to  the  Pacific  Ocean  for  this  purpose  and ;  it  is  to 
correct  these  observations  that  no  less  than  forty-six  expe- 
ditions were  sent  out  last  year  from  Europe  and  America. 
Halley  made   many  other  valuable  astronomical   observa- 


CH.  XIX.  H ALLEY'S   COMET.  163 

tions.'  He  was  the  first  astronomer  who  foretold  the  return 
of  a  comet.  Before  his  time  it  was  thought  that  they  went 
away  and  never  came  back  again ;  but  when  the  comet  of 
1682  appeared,  Halley  began  to  search  for  former  records 
of  comets  and  found  that  one  had  been  seen  about  every 
seventy-six  years,  reckoning  backwards  from  1682.  There- 
fore he  thought  these  must  all  be  the  same  comet,  and  he 
foretold  its  return  in  1758.  It  came  as  predicted,  and  has 
ever  since  been  called  '  Halley 's  comet'  Halley  died  in 
1742,  and  with  him  ends  the  astronomy  of  the  seventeenth 
century. 


Chief  Works  consulted. — Proctor's  '  Transits  of  Venus  j '  Herschel's 

*  Astronomy ; '  Denison's  *  Astronomy  without  Mathematics  ; '  Airy's 

*  Popular  Astronomy.' 


1 64  SEVENTEENTH  CENTURY,  rr.  iii. 


CHAPTER  XX. 

SCIENCE    OF   THE    SEVENTEENTH    CENTURY   (CONTINUED). 

Newton's  Discovery  of  the  Dispersion  of  Light — Traces  the  amount 
of  Refraction  of  each  of  the  Coloured  Rays — Makes  a  Rotating 
Disc  turning  the  colours  of  the  Spectrum  into  white  Light 
— Reason  why  all  Light  passing  through  glass  is  not  Coloured — 
Mr.  Chester  More  Hall  discovers  the  Difference  of  Dispersive  Power 
in  Flint  and  Crown  Glass — Newton's  Papers  destroyed  by  his  pet 
dog —  Last  years  of  Newton's  life. 

Newton  publishes  his  Discovery  of  the  Dispersion  of 
Light,  1671. — We  must  now  return  to  Newton,  and  consider 
his  third  great  discovery,  which  was  about  Hght.  You  will 
remember  that  he  had  to  wait  sixteen  years  between  his  first 
attempt  to  investigate  the  law  of  gravitation,  and  that  new 
measurement  of  the  earth  which  enabled  him  to  prove  the 
truth  of  his  theory.  During  this  time  he  had  by  no  means 
been  idle.  He  once  said  that  the  reason  he  had  succeeded 
in  making  discoveries  was  that  he  gave  all  his  attention  to 
one  subject  at  a  time  ;  from  1666  to  1671,  when  his  papers 
on  gravitation  were  quite  laid  aside,  the  subject  to  which  he 
devoted  himself  was  Light. 

In  the  early  part  of  the  seventeenth  century  several 
people  had  tried  to  find  out  what  it  was  that  gave  rise  to 
different  colours.  An  Italian  archbishop  named  Antonio 
de  Dominis  (died  1625)  had  given  a  better  explanation  of 
the  rainbow  than  Roger  Bacon  had  given  before  him ;  and 


ClI.   XX. 


THE  DISPERSION  OF  LIGHT. 


165 


Fig.  28. 


Descartes  had  gone  farther,  and  had  pointed  out  that  a  ray 
of  light  seen  through  a  clear,  angular,  polished  piece  of  glass, 
called  a  prism  (see  Fig.  28),  is  spread 
out  into  colours  exactly  like  the  rain- 
bow ;  but  no  one  had  yet  been  able 
to  say  what  was  the  cause  of  these  dif- 
ferent tints.  Newton  was  the  first  to 
work  this  out  in  his  usual  accurate  and  painstaking  way. 
He  tells  us  that  in  1666  he  'procured  a  triangular  glass 
prism,  to  try  therewith  the  celebrated  phenomena  of 
colours,'  and  in  the  very  first  experiment  he  was  struck  by  a 
very  curious  fact.     He  had  made  a  round  hole  f  (Fig.  29), 


Glass  Prism. 


Fig.  29. 


Newton's  first  Experiment  on  Dispersion  of  Light. 

D  E,  Window  shutter,     f,   Round  hole  in  it.     ABC,  Glass  prism.     M  N,  Wall  on 
which  the  spectrum  was  thrown. 

about  one-third  of  an  inch  broad,  in  the  window-shutter, 
D  E,  of  a  dark  room,  and  placed  close  to  it  a  glass  prism, 
A  B  c,  so  as  to  refract  the  sun-light  upwards  towards  the 
opposite  wall  of  the  room,  m  n,  making  the  line  of  colours 
(red,  orange,  yellow,  green,  blue,  indigo,  and  violet),  which 
Descartes  had  pointed  out,  and  which  Newton  called  a 
spectrum^  from  specto,  I  behold. 

While  he  was  watching  and  admiring  the  beautiful 
colours,  the  thought  struck  him  that  it  was  curious  the 
spectrum  should  be  long  instead  of  round.     The  rays  of 


1 


1 66  SEVENTEENTH  CENTURY.  pt.  hi. 

light  come  from  the  sun,  which  is  round,  therefore,  if  they 
were  all  bent  or  refracted  equally,  there  ought  to  be  a 
round  spot  upon  the  wall  ;  instead  of  which  it  was  long 
with  rounded  ends,  like  a  sun  drawn  out  lengthways.  What 
could  be  the  reason  of  the  rays  falling  into  this  long  shape  ? 
At  first  he  thought  that  it  might  be  because  some  of  them 
passed  through  a  thinner  part  of  the  prism,  and  so  were  less 
refracted ;  but  when  he  tested  this  by  sending  one  ray  through 
a  thin  part  of  the  prism,  and  another  through  a  thick  part, 
he  found  that  they  were  both  equally  spread  out  into  a 
spectrum.  Then  he  thought  that  there  might  be  some  flaw 
in  the  glass,  and  he  took  another  prism ;  still,  however,  the 
spectrum  remained  long,  as  before.  Next  he  considered 
whether  the  different  angles  at  which  the  rays  of  the  sun  fell 
upon  the  prism  had  anything  to  do  with  it,  but  after  calcu- 
lating this  mathematically  he  found  the  difference  was  too 
small  to  have  any  effect.  Finally,  he  tried  whether  it  was 
possible  that  the  rays  had  been  bent  into  curves  in  passing 
through  the  prism,  but  he  found  by  measurement  that  this 
again  was  not  the  reason. 

At  last,  after  carefully  proving  that  none  of  these  expla-. 
nations  was  the  true  one,  he  began  to  suspect  that  it  mus- 
be  something  peculiar  in  the  different  coloured  rays  them- 
selves, which  caused  them  to  divide  one  from  the  other. 
To  prove  this  he  made  the  following  experiment : — He  made 
a  hole,  F,  in  the  shutter,  as  before,  and  passed  the  light 
through  the  prism,  a  b  c,  throwing  the  spectrum  upon  a 
screen,  m  n.  He  then  pierced  a  tiny  hole  through  the  screen 
at  the  point  g,  Fig.  30  ;  the  hole  in  this  board  was  so  small 
that  the  rays  of  only  one  colour  could  pass  through  at  a 
time.  Newton  first  let  a  red  ray  pass  through,  so  that  it  v/as 
bent  by  the  prism,  h  i  k,  and  made  a  shaded  red  spot  on 


CH.  XX.         NEWTON— DISPERSION  OF  LIGHT. 


167 


the  wall  at  R  \  here  he  put  a  mark.  He  now  moved  the  first 
prism,  A  B  c,  a  little,  so  as  to  let  the  second,  or  orange  ray, 
pass  through  the  hole  g.  This  xsiy  fell  upn  exactly  the  same 
spot  of  the  second  prism,  h  i  k,  as  the  red  ray  had  done,  but 
it  did  not  go  to  the  same  spot  on  the  wall ;  it  was  more  bent  in 
passing  through  the  prism,  and  made  an  orange  spot  at  o. 

Fig.  30. 


Diagram  showing  the  Different  Refraction  of  Rays  of  Different  Colours. 

D  E,  Shutter.  F,  Round  hole,  a  b  c.  First  prism.  M  N,  Screen  receiving  the 
spectrum,  g.  Small  hole  through  which  the  rays  of  only  one  colour  can  pass. 
H  I  K,  Second  prism  refracting  those  rays. 

above  the  point  r.  By  this  Newton  knew  that  an  orange 
ray  is  more  refracted  in  passing  through  a  prism  than  a  red 
ray  is.  He  moved  his  prism,  a  b  c,  again,  so  as  to  let  the 
yellow  ray  through.  ^  This  was  still  more  bent,  and  fell  above 
o  on  the  point  y.  In  this  way  he  let  all  the  different 
coloured  rays  pass  through  the  hole,  marking  the  points  on 
which  they  fell,  and  he  found  that  each  ray  was  more  bent 
than  the  last  one,  till  he  had  marked  out  a  second  complete 
spectrum  on  the  wall.  Only  the  two  extreme  rays,  red  and 
violet,  are  traced  out  in  Fig.  30,  to  avoid  confusion. 

This  experiment  proved  clearly,  ist,  that  light  is  made  icp  of 
differently  coloured  rays ;  and  2nd,  that  these  rays  are  differently 
refracted  in  passing  through  a  prism.  The  red  rays  are  least 
bent,  and  the  violet  ones  most,  while  each  of  the  other  rays 


1 68 


SEVENTEENTH  CENTURY. 


PT.  III. 


between  these  have  their  own  course  through  the  prism.  I 
must  warn  you,  however,  not  to  think  that  there  are  exactly 
seven  colours  :  there  are  really  an  infinite  number,  passing 
gradually  into  each  other  j  Newton  only  divided  them 
roughly  into  seven  for  convenience. 

This  spreading  out  of  the  different  coloured  rays  is  called 
the  dispersion  of  light.  I  wish  I  could  give  you  the  many 
beautiful  experiments  which  Newton  made  to  prove  it,  but 
I  have  only  room  for  one,  which  you  can  easily  try  for 
yourself,  by  which  the  different  colours  which  make  up 
the  spectrum  can  be  turned  back  again  into  white  light. 
You  will  see  at  once  that  if  it  is  true  that  white  light  can 
be  divided  up  into  colours,  those  same  colours  when  re- 
united must  make  white.  To  show  this  Newton  took  a 
round  card  and  painted  upon  it  the  seven  colours,  as  pure  as 
possible,  five  times  over,  like  a  spectrum  five  times  repeated 
(a,  Fig.  31),  and  then  spun  it  round  rapidly,  so  that  the  eye 
received  the  impression  of  all  the  seven  colours  at  once 
(b,  Fig.  31).     If  you  do  this  you  will  see  the  card  looks  a 

Fig.  ^i. 


A,  Newton's  disc.    B,  Disc  rotating. 


dirty  white,  because  the  colours  blend  together  just  as  they 
do  in  a  ray  of  light.     You  will  not  get  a  pure  white,  because 


CH.  XX.  THE  ACHROMATIC   TELESCOPE,  169 

the  artificial  colours  are  not  pure,  and  also  because  it  is 
difficult  to  paint  each  colour  in  the  proper  proportion. 

But  now  that  we  have  proved  that  light  is  broken  up 
into  colours  in  passing  through  a  denser  medium,  you  may 
perhaps  ask  how  it  is  that  we  do  not  see  coloured  rays  when- 
ever we  look  at  the  sun  through  glass  or  any  other  trans- 
parent substance.  The  reason  is  that  when  the  two  sides  of 
the  glass  are  parallel  (that  is,  lie  always  at  the  same  distance 
from  each  other),  the  ray  of  light  is  bent  just  as  much  in 
going  out  from  the  glass  into  the  air  as  it  was  when  it  came 
in  from  the  air  into  the  glass,  and  so  it  remains  just  as  it  was 
at  first.  When  the  two  sides  are  not  parallel,  as  in  a  rounded 
lens,  colours  do  appear  in  the  thin  edges  of  the  glass,  and 
these  used  to  be  very  troublesome  in  telescopes  and  micro- 
scopes. Newton .  thought  that  they  could  never  be"  got  rid 
of,  for  he  did  not  know  that  light  is  spread  out  or  dispersed 
more  in  one  kind  of  glass  than  in  another.  But  two  years 
after  his  death,  in  1729,  Mr.  Chester  More  Hall,  of  Essex, 
found  that  two  kinds  of  glass  (flint-glass  and  crown-glass) 
disperse  light  differently,  so  that  when  you  put  them  together 
they  correct  each  other,  and  the  coloured  rays  at  the  edges 
are  blended  into  white  light.  Telescopes  and  microscopes 
which  are  made  in  this  way  are  called  achroinatic  (from  a, 
without ;  chroma^  colour).  A  patent  for  such  instruments  was 
taken  out  by  a  Mr.  Dollond  in  1757,  and  he  probably  in- 
vented them  without  having  heard  of  Mr.  Hall's  discover}'-. 

It  would  require  a  whole  volume  to  give  you  all  Newton's 
investigations  into  the  nature  of  light,  and  his  experiments 
on  the  coloured  rings  of  the  soap-bubble  and  other  trans- 
parent substances.  His  work  on  Optics  was  read  before  the 
Royal  Society  in  167 1  and  1672,  but  the  ideas  were  so  new 
that   many   clever  men,  who   should   have   known  better, 

9 


lyo  SEVENTEENTH  CENTURY.  pt.  hi. 

attacked  him  with  a  number  of  foohsh  and  ignorant  ob- 
jections, till  at  last  he  told  his  friend  Huyghens  that  he  was 
almost  sorry  he  had  ever  made  them  public. 

After  his  great  work,  the  '  Principia,'  had  been  published 
in  1687,  he  next  turned  his  attention  to  chemistiy,  but  un- 
fortunately all  the  results  of  his  labour  in  this  science  were 
destroyed  by  an  accident.  One  day  when  he  was  in  chapel, 
his  pet  dog  Diamond  turned  over  a  lighted  taper,  which  set 
fire  to  all  the  papers  on  which  his  work  was  written.  When 
he  returned  and  found  the  charred  heap  it  is  said  that  he 
merely  exclaimed,  *  Oh  Diamond,  Diamond  !  thou  little 
thinkest  the  mischief  thou  hast  done  ! '  but  his  grief  at  the 
loss  of  his  work  affected  his  brain,  and  though  he  re- 
covered and  lived  another  forty  years,  publishing  many 
editions  of  his  works,  yet  he  never  made  any  more  great 
discoveries. 

Newton  received  many  honouiG  in  his  old  age  :  in  1699 
he  was  elected  Master  of  the  Mint,  and  a  member  of  the 
French  Royal  Academy  of  Sciences ;  in  1703  he  was  made 
President  of  the  Royal  Society,  and  in  1705  he  was  knighted 
by  Queen  Anne.  Like  all  truly  great  men,  he  was  modest 
as  to  his  own  abilities,  and  always  willing  to  be  taught  by 
others.  He  felt  so  strongly  how  much  we  have  still  to 
learn  about  the  Universe,  that  he  considered  his  own  dis- 
coveries as  very  trifling  indeed.  A  short  time  before  his 
death  he  said  of  himself,  *  I  know  not  what  the  world  may 
think  of  my  labours  ;  but  to  myself  I  seem  to  have  been  only 
like  a  boy  playing  on  the  sea-shore,  and  diverting  myself  in 
now  and  then  finding  a  smoother  pebble  or  a  prettier  shell 
than  ordinary,  whilst  the  great  ocean  of  truth  lay  all  un- 
discovered before  me.'  Yet  this  man  who  spoke  so  humbly 
was  the  discoverer  of  the  greatest  and  most  universal  lav/ 


CH.  XX.  DEATH  OF  NEWTON.  171 

known  to  mankind  !  He  loved  to  seek  out  new  laws,  but  he 
was  more  anxious  to  collect  facts  and  to  make  sure  that  he 
was  right,  than  eager  to  publish  his  conclusions.  It  was  the 
truth  he  loved,  and  not  the  fame  which  it  brought.  His 
patience  and  perseverance  were  unbounded ;  he  was  never 
in  a  hurry,  but  turned  a  subject  over  and  over  in  his  mind, 
for  years  together,  seizing  upon  every  new  light  shed  upon 
it,  and  waiting  patiently  for  more.  And  through  all  his 
labours  he  looked  reverently  up  to  the  One  Great  Light 
whose  guiding  power  he  loved  to  trace  and  to  acknowledge 
in  all  the  wonders  of  the  universe.  He  died  in  1727  at 
eighty-five  years  of  age,  and  was  buried  in  Westminster 
Abbey,  his  pall  being  borne  by  the  first  nobles  of  the  land. 


Chief  Works  consulted.  —  Newton's  'Optics,'  1721  j  Ganot's 
'Physics;'  Rossiter's  'Physics;'  Brewster's  'Encyclopaedia,'  art. 
*  Optics ; '  Herschel's  *  Familiar  Lectures.* 


172  SEVENTEENTH  CENTURY.  pt.  hi. 


CHAPTER  XXI. 

SCIENCE   OF   THE    SEVENTEENTH    CENTURY    (CONTINUED). 

Roemer  measures  the  Velocity  of  Light— Newton's  Corpuscular  Theory 
of  Light — Undulatory  or  Wave-theory  proposed  by  Huyghens  — 
Invention  of  Cycloidal  Pendulums  by  Huyghens — Discovery  of 
Saturn's  Ring — Sound  caused  by  Vibration  of  Air — Light  by  Vibra- 
tion of  Ether — Reasons  why  we  see  Light — Reflection  of  "Waves  of 
Light — Cause  of  Colour — Refraction  explained  by  the  Undulatory 
Theory — Mr.  Tylor's  Illustration  of  Refraction — Double  Refraction 
explained  by  Huyghens  -Polarisation  of  Light  not  understood  till 
the  nineteenth  century. 

Olaus  Eoemer  measures  the  Velocity  of  Light,  1676.— 

While  Newton  was  dispersing  light  in  prisms,  and  finding 
out  its  nature,  Olaus  Roemer,  a  famous  Danish  astronomer 
(born  1644,  died  17 10),  was  engaged  in  something  almost 
as  wonderful.  He  was  measuring  the  rate  at  which  light 
travels  across  the  sky !  It  seems  at  first  as  if  this  would 
be  impossible,  but  we  now  know  three  different  ways  of 
accomplishing  it ;  Roemer's  was  the  first  attempt  ever 
made,  and  his  measurement  was  very  near  indeed  to  the 
truth. 

You  will  remember  that  Jupiter  has  four  moons,  which 
move  round  it  as  our  moon  moves  round  our  earth.  Three 
of  these  moons  are  so  near  Jupiter  and  move  round  it  in 
such  a  manner  that  they  pass  through  its  shadow  and  are 
eclipsed  every  time  they  go  round.     Now  it  became  very 


cii.  XXI.  VELOCITY  OF  LIGHT.  173 

useful,  for  certain  astronomical  reasons,  to  know  exactly  when 
these  eclipses  happened,  and  the  time  of  their  occurrence 
was  therefore  calculated  very  carefully  ev^  since  Galileo 
first  discovered  them.  There  was  no  difficulty  in  doing  this, 
and  yet,  strange  to  say,  the  eclipses  rarely  happened  exactly 
at  the  right  moment.  Sometimes  they  were  too  early,  some- 
times too  late,  and  they  varied  according  to  some  regular 
rule  as  much  as  16  minutes  36  seconds  on  each  side  of  the 
exact  moment  when  they  ought  to  have  happened. 

At  last  it  occurred  to  Roemer,  and  to  an  Italian  astrono- 
mer named  Cassini,  that,  as  Jupiter  is  farther  away  from  the 
earth  at  one  time  than  at  another,  the  eclipses  might  be  seen 
some  minutes  later  whenever  the  rays  of  light  from  the 
moons  had  to  cross  a  greater  distance  to  reach  the  earth. 
Cassini  seems  to  have  put  the  thought  aside  and  not  to  have 
worked  it  out ;  but  Roemer  seized  upon  it,  and  by  careful 
calculations  proved  that  it  was  the  tme  answer  to  the  diffi- 
culty. If  the  earth  was  at  e  (Fig.  32)  for  example,  when  Jupiter 

Fig.  32. 


Diflferent  Distances  at  which  Jupiter's  Light  reaches  the  Earth. 
J,  Jupiter.    E  e'.  The  earth. 

was  at  J,  the  light  would  not  have  nearly  so  far  to  travel  as  if 
the  earth  was  at  e'  ;  and  in  this  last  position  the  16  minutes 
36  seconds  would  be  taken  up  by  the  light  crossing  the 
earth's  orbit  from  e  to  e'.  This  distance  was  known  to  be 
about  190,000,000  miles,  so  that  light  travels  at  the  rate 


174  SEVENTEENTH  CENTURY.  pt.  hi. 

of  190,000,000  miles  in  996  seconds,  or  about  190,000 
miles  in  a  second.  This  is  seven  million  times  as  fast  as  the 
quickest  express  train. 

Huyghens  and  Newton — Theories  of  Light. — The  time 
had  now  come  when  so  much  was  known  about  the  way  in 
which  light  behaves,  that  philosophers  began  to  ask  them- 
selves, '  What  is  Light?' — a  question  by  no  means  so  easily 
answered  as  you  may  think  ;  for  though  it  is  by  means  of 
light  that  we  see  everything,  yet  light  in  itself  is  invisible. 
You  will  exclaim  at  once  that  you  can  see  a  sunbeam 
shining  through  a  crack  in  a  window- shutter.  But  what  you 
see  is  not  light  itself,  it  is  the  particles  of  dust  or  smoke 
which  are  acted  upon  by  light  so  that  they  shine.  There  is 
one  very  simple  way  of  proving  to  yourself  that  rays  of  light 
are  not  visible  lines.  When  the  moon  is  shining  you  know 
that  it  is  reflecting  the  light  of  the  sun,  therefore  there  must 
be  light  crossing  the  sky  and  falling  upon  its  surface.  But 
now  look  up  some  other  night  when  the  moon  is  not  there. 
All  is  darkness ;  yet  the  light  must  be  there  just  the  same, 
and  would  have  caused  the  moon  to  shine  if  it  had  been 
there  also,  but  as  there  is  nothing  to  reflect  it  to  your  eye  it 
is  invisible. 

What,  then,  is  this  light,  invisible  in  itself,  yet  without 
which  we  can  see  nothing?  Newton  thought  that  it  was 
composed  of  minute  invisible  particles  of  matter  which 
darted  out  in  straight  lines  from  luminous  or  light-giving 
bodies,  and  falling  upon  our  eyes  caused  the  sensation  which 
we  call  light.  This  is  called  the  Corpuscular^  or  sometimes 
the  Emission,  Theory  of  Light.  It  was  very  ingenious,  and 
accounted  for  a  great  many  of  the  facts,  but  there  were 
many  others  which  it  did  not  explain ;  and  I  will  not 
attempt  to  describe  it  to  you,  because  another  theory,  called 


CH.  XXI.  VARIOUS   THEORIES  OF  IIGHT.  175 

the  Undulatory  {or  Wave)  Theory  of  Lights  has  now  been 
found  to  be  much  more  complete  and  satisfactory.  This 
last  theory  was  first  proposed  by  a  Dutch  mathematician 
and  astronomer  named  Christian  Huyghens,  the  son  of 
Constantine  Huyghens,  Counsellor  to  the  Prince  of  Orange. 

Christian  Huyghens  was  born  at  the  Hague,  in  Holland, 
in  the  year  1629  ;  when  he  was  only  thirteen  years  old  he 
was  already  passionately  fond  of  mathematics,  and  ex- 
amined every  piece  of  machinery  that  fell  in  his  way.  He 
received  a  very  good  education,  and  wrote  some  able  treatises 
upon  geometry  when  he  was  only  two-and- twenty.  From 
this  time  he  advanced  very  rapidly,  both  writing  valuable 
papers  and  making  grand  discoveries.  In  1658  he  invented 
a  peculiar  kind  of  pendulum  called  the  cycloidal  pendulum, 
which  would  keep  accurate  time  when  swinging  over  wide 
spaces  ',  and  he  was  also  the  first  to  apply  pendulums  to 
clocks.  In  1659  he  made  a  telescope  ten  feet  long,  with 
which  he  discovered  one  of  Saturn's  satellites,  and  described 
accurately  Saturn's  ring,  which  Galileo  had  mistaken  for  two 
stars.  In  1660  he  came  to  England,  and  solved  some 
questions  which  the  Royal  Society  had  proposed  about 
the  laws  of  motion.  Then  he  was  invited  to  settle  in  France, 
and  it  was  there,  in  1678,  that  he  read  before  the  '  Academie 
des  Sciences  '  the  theory  of  light  which  we  must  now  try  to 
understand. 

Undulatory  Theory  of  Light,  1678.— I  must  first  tell 
you  that  Newton,  among  his  many  other  investigations,  had 
shown  that  sound  is  caused  by  a  trembling  or  vibration  of 
the  air.  Thus,  when  you  strike  the  wire  of  a  harp,  the 
trembling  of  the  string  shakes  the  air,  and  the  quivering 
motion  travels  along  like  waves  upon  a  pond,  until  some 
wave  strikes  the  drum  of  your  ear  and  produces  the  sen- 


176  SEVENTEENTH  CENTURY.  pt.  iit. 

sation  we  call  sound.  The  tighter  and  shorter  the  string,  is, 
the  more  rapid  the  vibrations  or  waves  will  be,  and  the 
more  shrill  will  be  the  note  which  you  hear. 

Now  Huyghens  said, '  We  can  only  explain  light  by  sup- 
posing it  to  be  a  vibi-ation  like  sound.'  But  here  at  the 
very  outset  came  a  difficulty.  We  know  that  light  is  not  a 
vibration  of  the  air,  for  if  you  draw  the  air  completely  out  of 
a  glass  vessel,  light  will  still  pass  across  it;  and  besides,  we  g^t 
light  from  the  sun  and  the  distant  stars,  so  that  it  has  to 
come  across  a  great  airless  space  before  it  reaches  the  at- 
mosphere of  our  earth.  And  yet,  if  light  is  a  vibration,  it  is 
clear  there  must  be  something  between  the  sun  and  us  to 
vibrate.  To  meet  this  difficulty  Huyghens  supposed  the 
whole  of  space  between  our  earth  and  the  most  distant  stars  to 
be  filled  with  an  elastic  invisible  suhsta7tce  which  he  called 
^  ether. ^  He  assumed  this  substance  to  be  so  fine  and 
subtle  that  it  passes  between  the  atoms,  even  of  solid 
objects,  and  that  the  sun  and  all  luminous  bodies  cause  it 
to  vibrate  so  that  its  undulations  or  waves  strike  upon  our 
eyes  and  give  rise  to  the  sensation  we  call  light. 

Thus,  according  to  this  theory,  when  you  look  at  the 
sun,  the  invisible  '  ether '  filling  the  whole  space  between  you 
and  it,  is  moving  up  and  down  in  rapid  vibrations,  just  as  if 
the  sun  held  one  end  of  a  cloth  and  you  the  other,  and  the 
sun  was  shaking  the  cloth  so  that  the  waves  travelled  along 
it  to  your  eye  ;  and  every  wave  that  hit  you  would  cause 
the  sensation  called  light. 

This  theory  explains  very  well  how  light-waves  may  be 
in  the  sky  and  yet  we  may  not  see  them  ;  for  if  a  stick 
is  moving  rapidly  to  and  fro  in  the  air,  and  you  go  within 
reach  of  it  you  feel  pain,  but  if  you  keep  out  of  reach  no 
pain  is  produced.     In  the  same  way,  when  the  vibration  of 


CH.  XXI.  THE   UNDULATORY  THEORY.  177 

this  invisible  ether  strikes  your  eye  you  feel  light,  but 
though  the  waves  may  be  travelling  rapidly  across  the  sky. 
so  long  as  they  do  not  fall  upon  your  eye,  no  light  will  be 
produced  to  you. 

But  suppose  you  were  not  looking  at  the  sun,  but  at  the 
ground,  why  should  you  still  see  ?  Because  the  waves  from 
the  sun  which  strike  the  ground  cannot  travel  on  so  easily 
through  the  solid  earth  as  through  the  pure  ether,  so  a  great 
number  of  them  bound  off  and  vibrate  back  along  the  ether 
again,  from  the  ground  to  your  eye  ;  and  as  they  vibrate  dif- 
ferently according  as  the  ground  is  rough  or  smooth,,  hard  or 
soft,  wet  or  dry,  they  make  a  different  impression  upon  your 
eye,  and  cause  you  to  see  a  picture  of  the  ground  as  it  is. 

Clear  white  glass  and  other  perfectly  transparent  bodies 
let  nearly  all  the  waves  of  light  pass  through  them  and  send 
hardly  any  back  to  your  eye  ;  and  people  have  in  conse- 
quence been  known  to  walk  right  up  against  glass  doors  with- 
out seeing  them.  Bright  polished  surfaces,  on  the  contrary, 
like  steel  and  mercury,  turn  nearly  all  the  waves  back  again, 
and  this  is  why  we  see  our  own  faces  reflected  so  clearly  in 
a  looking-glass,  where  it  is  the  mercury  at  the  back  which  is 
the  real  mirror. 

If  we  had  room  we  might  follow  out  these  light-vibrations 
in  a  very  interesting  manner.  For  instance,  why  does  a 
leaf  look  green  and  a  soldier's  coat  red?  Because,  as  in 
sound  the  kind  of  note  you  hear  depends  upon  the  quick- 
ness of  the  vibrations  of  the  air,  so  in  light  it  depends  upon 
the  quickness  of  the  vibrations  of  the  ether  what  colour  you 
see.  The  vibrations  which  produce  violet,  indigo,  blue, 
green,  yellow,  orange,  and  red,  have  travelled  all  together  as 
white  light  through  the  ether,  but  they  are  differently  treated 
by  the  leaf     All  except  the  green  waves  are  quenched,  or 


178  SEVENTEENTH  CENTURY.  pt.  in. 

absorbed  2JS>  it  is  called,  by  the  material  of  the  leaf,  and  only 
the  green  waves  bound  back  upon  your  eye.  In  other  words, 
the  vibrations  of  the  ether  coming  from  the  leaf  move  exactly 
fast  enough  to  produce  upon  your  eye  the  sensation  you  call 
green^  just  as  the  vibration  of  the  air  caused  by  a  particular 
string  of  a  harp  produces  on  your  ear  the  sensation  of  the 
note  you  call  the  middle  C. 

Refraction  of  Light  explained  by  Hnyghens. — But  we 
must  now  go  back  to  Huyghens,  and  point  out  how  beauti- 
fully he  explained  by  his  undulatory  theoiy  the  refraction  or 
bending-back  of  rays  of  which  we  have  already  spoken  so 
much.  When  a  wave  of  light  is  travelling  onwards,  he  said, 
if  it  passes  vertically  into  glass  or  any  denser  substance,  the 
wave  will  move  more  slowly,  but  it  will  still  go  straight  on, 
because  both  ends  of  th  :^  wave  will  be  equally  checked.  But 
if  the  wave  goes  into  the  glass  obliquely  (see  p.  47),  one  end 
of  it  will  reach  the  glass  first  before  the  other,  and  will  move 
slowly,  while  the  other  end  goes  on  unchecked,  and  so  the 
wave  will  swing  round  and  will  have  its  direction  altered. 
In  the  same  way,  when  it  passes  out  again  from  the  glass, 
one  end  will  pass  out  first,  and  will  move  more  easily  in  the 
air  than  the  end  that  is  still  in  the  glass,  and  so  it  will  swing 
round  again  and  make  another  bend. 

You  must  not  be  disappointed  if  you  do  not  understand 
this  at  once,  for  it  is  very  difficult  \  to  make  it  easier  we  will 
borrow  a  very  ingenious  illustration  given  last  year  (Jan.  i, 
1874)  by  Mr.  E.  B.  Tylor,  in  a  periodical  called  'Nature.' 
Take  two  small  wheels  about  2  inches  round,  and  mount 
them  loosely  upon  a  stout  iron  axle  measuring  about  half-an- 
inch  round.  This  will  make  a  runner  like  two  wheels  of  a 
cart,  and  if  you  let  it  roll  down  a  smooth  board  it  will  repre- 
sent very  fairly  the  crests  or  tops  of  the  waves  of  light  in 


CH.  XXI.        DOUBLE  REFRACTION  OF  LIGHT. 


179 


Fig.  33. 


the  ether.  Let  your  board  be  about  2  J  feet  long,  and  at  one 
end  of  it  glue  on  pieces  of  thick-piled  velvet  of  the  shape 
of  lenses  (see  i,  2,  3,  Fig.  zz\  Let  your  runner  first 
go  straight  down  the  board 
upon  the  velvet;  it  will  then 
run  through  the  velvet  with- 
out changing  its  course,  as  a 
vertical  ray  does  through  a 
lens.  Then  start  it  obliquely 
across  the  board  so  that  it  will 
reach  the  lens  i  in  the  position 
B.  Here  the  left  wheel  of  the 
runner  will  touch  the  velvet 
first,  and  will  be  checked  by 
the  rough  pile,  while  the  right 
wheel  moves  on  quickly  as  be- 
fore, and  thus  the  runner  will 
swing  round  or  be  refracted 
towards  the  thick  part  of  the 
lens.  Then,  as  it  passes  out 
again  the  right  wheel  will  come 
out  of  the  velvet  first  and  will 
move   more   quickly   on    the 


-::%''" 


Figures  illustrating  the  passage  of  the 
waves  of  light  through  difFerent- 
shaped  lenses  (Tylor). 


smooth  board,  while  the  left  is  still  checked  by  the  velvet  at 
c ;  therefore  the  runner  will  again  be  shifted  round  or  re- 
fj-aded  as  it  passes  out.  You  can  easily  foUoAV  the  course 
of  the  runner  through  the  other  lenses  for  yourself,. always 
noticing  that  the  arrow  marks  which  way  the  ray  of  light  is 
coming;  and  when  you  have  done  this  you  will  have  a 
beautiful  imitation  of  the  way  in  which  the  waves  of  light 
are  refracted  in  passing  through  different  mediums. 

Double  Refraction. — There  is  still  one  more  remarkable 


i8o  SEVENTEENTH  CENTURY.  ft.  hi. 


fact  about  light  which  Huyghens  explained;  namely,  the 
double  refraction  of  light  through  a  crystal  called  Iceland  spar. 
A  physician  of  Copenhagen  named  Erasmus  Bartholinus  had 
received  from  Iceland  a  crystal  in  the  form  of  a  rhomboid 
(see  Fig.  34),  which,  when  broken,  fell  into  pieces  of  the 
same  shape.     Bartholinus    called   this 

Fig.  34.  ^ 

. 7         crystal  '  Iceland  spar,'  and  while  mak- 


Z®         /  ing  experiments   with   it    he   observed 

/  that  an  inkspot   or   any   small  object 

A  spot  of  ink  seen  through  a   seen  through  it  appeared  to  be  doubled. 

crystal  of  Iceland  spar.  ° 

He  was  not  able  to  explain  this  curious 
fact,  but  he  published  an  account  of  it  in  1669,  and  Huy- 
ghens accounted  for  it  quite  correctly  by  suggesting  that  the 
crystal  was  more  elastic  in  one  direction  than  in  the  other, 
so  that  a  wave  of  light  passing  into  it  was  divided  into  two 
waves  moving  at  differeat  rates  through  the  crystals.  This 
would  cause  them  to  be  bent  differently— one  according  to 
Snell's  ordinary  law  of  refraction  (see  p.  107),  and  the  other 
in  an  extraordinary  way.  Thus  these  two  separate  rays  fall- 
ing upon  the  eye  would  cause  there  the  impression  of  two 
objects. 

This  curious  effect  is  very  interesting  to  study,  and  it  led 
Huyghens  to  make  a  number  of  remarkable  experiments. 
He  found  that  the  two  rays  when  they  passed  out  at  the 
other  side  of  the  crystal  remained  quite  separate  the  one  from 
the  other,  and  if  they  were  afterwards  sent  through  another 
crystal  in  the  same  direction  that  they  had  gone  through  the 
first,  they  went  on  each  their  own  way.  But  now  came  a  very 
extraordinary  fact :  if  the  second  crystal  was  turned  round 
a  little  so  that  the  rays  passed  in  rather  a  different  direction 
through  it,  each  ray  was  again  split  up  into  two,  so  that  there 
w^ere  now  four  rays,  sometimes  all  equally  bright,  sometimes 


cir.  XXI,  POLARIZATION  OF  LIGHT.  18 1 

of  unequal  brightness,  but  the  light  of  all  four  was  never 
greater  than  the  light  of  the  one  ray,  out  of  which  they  had 
all  come.  These  four  rays  continued  apart  while  he  turned 
the  second  crystal  more  and  more  round  ;  till,  when  he  had 
turned  it  90°,  or  a  quarter  of  a  circle,  the  rays  became  two 
again,  with  this  remarkable  peculiarity,  that  they  had  changed 
characters  !  The  ray  which  before  had  been  refracted  in 
the  ordinary  way  now  took  the  extraordinary  direction,  while 
the  other  chose  the  ordinary  one. 

This  curious  effect  observed  by  Huyghens  is  now  known 
as  the  ^ ;polai'ization  of  light '  by  crystals.  It  is  very  difficult 
to  understand,  and  you  must  be  content  at  present  to  know 
that  he  discovered  the  fact.  There  is  a  beautiful  explanation 
of  it,  but  we  must  wait  for  that  till  we  consider  the  science 
of  the  nineteenth  century,  for  it  is  now  much  better  under- 
stood. Huyghens'  *  Theory  of  Light '  was  published  in  1690, 
under  the  title  '  Traite  de  la  Lumiere.'  He  remained  in 
Paris  for  some  years  -,  but  left  it  and  returned  to  Holland 
when  the  persecution  of  the  Protestants  began  after  the 
revocation  of  the  Edict  of  Nantes.     He  died  in  1695. 


Chief  Works  consulted.  —  Ilerschel's  '  Familiar  Lectures  '  —  art. 
'Light;'  Tylor,  <  On  Refraction'— *  Nature,'  vol.  ix.  ;  *  Edin.  Phil. 
Journal,' vols.  ii.  and  iii. — 'On  Double  Refraction;'  Ganot's  'Phy- 
sics ;'  Encyclopjedias— '  Britannica,'  '  Metropolitana,'  and  Brewster's. 


1 82  SEVENTEENTH  CENTURY.  ft.  hi. 


CHAPTER  XXIL 

SUMMARY    OF   THE    SCIENCE   OF   THE   SEVENTEENTH 
CENTURY. 

We  have  now  arrived  at  the  close  of  the  seventeenth  century, 
and  it  only  remains  for  us,  before  going  farther,  to  try  and 
picture  to  ourselves  the  great  steps  in  advance  which  had 
been  made  between  the  years  1600  and  1700.  We  saw  at 
p.  82  that  the  work  of  the  sixteenth  century  consisted 
chiefly  in  making  men  aware  of  their  own  ignorance,  and 
teaching  them  to  inquire  into  the  facts  of  nature,  instead  of 
merely  repeating  what  they  had  heard  from  others.  In  the 
seventeenth  century  we  find  them  following  out  this  rule  of 
patient  research,  and  being  rewarded  by  arriving  at  grand 
and  true  laws. 

Astronomy. — To  begin  with  Astronomy.  Here  Galileo 
led  the  way  with  his  telescope.  The  structure  of  the  moon, 
with  its  mountains  and  valleys ;  the  existence  of  Jupiter's 
four  moons  revolving  round  it  and  giving  it  light  by  night ; 
the  myriads  of  stars  of  the  Milky  Way  j  the  spots  of  the  sun 
coming  into  view  at  regular  intervals,  and  thus  proving  that 
the  sun  turns  on  its  axis  ;  all  these  discoveries  forced  upon 
men's  minds  the  truth  that  our  little  world  is  not  the  centre 
of  everything,  but  a  mere  speck  among  the  millions  of 
heavenly  bodies.  But  while  they  humbled  man's  false  pride 
in  his  own  importance,  they  taught  him  on  the  other  hand 
the  true  greatness  which  God  has  put  in  his  power  by  giving 


CH.  XXII.  SUMMARY.  1S3 

the  intellect  to  discover  and  understand  these  wonderful 
truths  if  he  will  only  seek  them  in  an  earnest  and  teachable 
spirit. 

Then  came  Kepler  with  a  still  grander  lesson,  for  he 
showed  that  the  movements  of  the  planets  are  governed  by 
regular  and  fixed  laws,  which  can  be  traced  out  so  accurately 
that  an  astronomer  is  able  to  foretell  with  confidence  what 
will  happen  many  years  after  he  himself  has  passed  away. 
Thus  we  see  Gassendi  and  Horrocks,  by  the  use  of  Kepler's 
labours,  calculating  within  a  few  minutes  the  time  of  a 
planet's  passage  across  the  face  of  the  sun  and  watching  the 
exact  fulfilment  of  the  prediction.  Nor  is  this  all  :  so  exact 
and  true  are  these  movements,  and  so  completely  is  man 
able  to  read  them  rightly,  that  by  this  simple  passage  of  a 
small  black  spot  across  the  sun  Halley  showed  that  we  may 
actually  number  the  millions  of  miles  between  ourselves  and 
the  great  light  around  which  we  move.  We  might  almost 
think  that  we  had  now  travelled  as  far  as  man's  mind  could 
go,  but  something  far  greater  remained  behind.  Newton 
sitting  under  his  apple-tree  and  pondering  on  the  wonderful 
mechanism  of  the  heavens,  found  the  one  great  law  which 
accounts  for  the  movements  of  all  the  bodies  in  the  universe 
— a  law  which  explains  equally  why  a  pin  falls  to  the  ground 
and  why  a  comet  which  has  been  lost  from  sight  for  more 
than  a  hundred  years  will  return  to  a  certain  fixed  spot  at  a 
day  and  an  hour  which  can  be  accurately  foretold.  "  Kepler 
had  pointed  out  fixed  and  definite  laws  by  which  the  uni- 
verse is  governed ;  Newton  demonstrated  that  one  law  ex- 
plains them  all.  He  showed  us  how  one  single  thought,  as 
it  were,  of  the  Divine  mind  suffices  to  govern  the  most 
complicated  as  well  as  the  simplest  movements  of  our 
system. 


1 84  SEVENTEENTH  CENTURY,  pt.  m. 

All  this  advance  from  Galileo  to  Newton  was  the  work 
of  the  seventeenth  century.  It  began,  you  see,  with  certain 
simple  facts  j  by  Galileo  seeing  that  bodies  existed  in  the 
heavens  which  were  not  known  to  be  there  before  ;  it  ended 
in  the  beautiful  law  of  which  we  have  just  spoken.  But  I 
want  you  particularly  to  notice  that  this  end  would  never 
have  been  reached  by  men  who  were  content  to  sit  down 
idly  and  talk  of  the  greatness  of  God.  It  was  the  result  of 
real  work  by  men  who  tried  first  to  learn  the  facts,  and  from 
these  to  prove  reverently  the  way  in  which  it  pleases  God  to 
bring  them  about ;  and  in  this  labour  of  love,  being  brought 
face  to  face  with  the  infinite  grandeur  of  nature,  they  learnt 
that  true  humility  which  led  Newton,  the  greatest  of  them 
all,  to  feel  that  he  was  but  as  a  little  child  gathering  pebbles 
on  the  shore  of  the  great  ocean  of  truth. 

Physics. — If  we  now  turn  to  Physics,  we  shall  find  that 
the  way  to  knowledge  lay  still  along  the  same  road  of  patient 
inquiry.  Torricelli's  barometer  and  Guericke's  hemispheres 
of  Magdeburg  both  proved  by  direct  experiment  that  the 
atmosphere  round  our  earth  is  pressing  downwards  with 
great  weight ;  and  this  again  brings  us  round  to  the  force  of 
gravity,  which  is  the  cause  of  this  weight;  while  Boyle's  ex- 
periment showed  that  air  is  elastic,  being  compressed  in 
exact  proportion  as  the  weight  upon  it  is  increased,  and  ex- 
panding again  directly  it  is  diminished. 

Again,  in  the  subject  of  Light,  we  begin  with  hard  dry 
facts,  which  doubtless  you  may  have  thought  it  wearisome  to 
master,  but  we  end  with  a  theory  so  wonderful  and  beautiful 
that  it  seems  more  like  a  fairy-tale  than  sober  science.  The 
first  step  here  was  the  invention  of  the  telescope,  which, 
while  it  opened  the  road  on  the  one  hand  to  astronomical 
discoveries,  also  led  to  the  grinding  of  lenses,  and  to  a  more 


CH.  XXII.  SUMMARY.  185 

careful  study  of  the  laws  of  light.  This  it  was  which  caused 
Snellius  to  make  experiments  on  the  bending  of  rays  with  a 
view  to  improving  telescopes,  and  so  to  discover  the  law  of 
refraction,  afterwards  more  fully  stated  by  Descartes.  Then 
we  find  this  last  philosopher  trying  to  explain  the  rainbow, 
and  studying  the  colours  falling  through  a  prism,  and  so  the 
subject  passed  on  into  the  hands  of  Newton. 

Here,  by  experiment  again,  the  threads  of  light  were  dis- 
entangled in  the  prism,  and  Newton  drew  out  its  many- 
coloured  rays,  tracing  them  one  by  one  on  their  road,  till  he 
had  shown  that  refraction  explained  them,  and  that  to  this 
law,  which  seemed  so  uninteresting  at  first,  we  owe  all  the 
lovely  colours  which  surround  us.  And  now  Huyghens 
takes  up  the  story  and  leads  us  fairly  into  the  invisible 
world.  This  light,  which  Roemer  had  proved  to  be  travel- 
ling across  space  with  marvellous  speed,  Huyghens  shows 
to  be  no  actual  substance  at  all,  but  most  probably  a 
trembling  of  an  invisible  and  intangible  ether — a  succession 
of  infinitely  tiny  waves  chasing  each  other  across  millions  of 
miles,  and  striking  at  last  on  the  minute  opening  of  our  eye, 
bringing  to  us  the  wonderful  effects  of  light.  As  Newton 
traced  colours,  so  Huyghens  traces  the  invisible  waves  through 
many  substances,  showing  us  their  path  and  why  they  take 
it  j  and  landing  us  at  last  in  the  bewildering  effects  of  polar- 
ization, leaves  us  there  to  wait  for  more  knowledge  in  a 
future  century. 

Biology. — And  now  we  come  to  Biology,  or  the  study  of 
all  those  sciences  which  relate  to  life.  Here  you  must  re- 
member that  our  account  of  the  discoveries  made,  must  be 
more  than  usually  imperfect,  because  the  subject  is  more  than 
usually  difficult.  Yet  we  can  form  some  idea  of  the  new 
light  thrown  upon  the  nature  of  the  living  body,  by  Harvey's 


i86  SEVENTEENTH  CENTURY.  pt.  hi. 


theory  of  the  circulation  of  the  blood  and  the  discoveries 
which  followed  concerning  the  way  in  which  nourishment  is 
carried  to  it.  We  can  see  how  Mayow's  experiments, 
proving  that  part  of  the  air  is  burnt  within  us,  supplying  heat 
to  our  bodies,  would  have  been  a  grand  step  in  advance  if 
he  had  lived  to  make  them  more  known,  and  how,  indeed, 
they  did  influence  those  who  came  after,  though  his  name 
was  for  a  time  forgotten.  More  clearly  still  we  can  under- 
stand how  Malpighi's  and  Grew's  investigations  with  the 
microscope,  bringing  to  light  hidden  parts  and  vessels  of  the 
human  frame,  gave  rise  to  a  totally  new  branch  of  science, 
and  enabled  men  to  study  the  organisation  of  their  own 
bodies  with  an  accuracy  quite  impossible  before  ;  while  the 
same  method  applied  to  Botany  gave  the  first  real  insight  into 
the  structure  of  plants,  tracing  out  their  delicate  organs,  and 
even  the  tiny  cells  of  which  their  flesh  is  composed.  And 
lastly,  in  the  field  of  Natural  History,  we  find  that  Ray  and 
Willughby  performed  the  immense  task  of  classifying  the 
whole  animal  and  vegetable  kingdoms,  and  laid  the  founda- 
tion of  the  grand  generalizations  of  Linnaeus  in  the  next 
century. 


SCIENCE    OF    THE 
EIGHTEENTH    CENTURY 


Chief  Men  of  Science  in  the  Eighteenth  Centtcry. 


A.D. 

Boei-hacave 1 668-1 738 

Hales 

I677-I76I 

Haller 

1 708-1 777 

Hunter 

1 728-1 793 

Bonnet 

1 720-1 793 

Spallanzani 

1 729-1 799 

Buffon 

I 707-1 788 

Linnaeus 

1707-1778 

Lazzaro  Moro 

1687     — 

Werner 

1750-1817 

Hutton 

1 726-1 797 

William  Smith 

% 

1 769-1839 

Black 

.     I 728-1 792 

Bergmann    . 

•     1 735-1 784 

Cavendish   . 

.     1731-1810 

Priestley 

I 733-1804 

Scheele 

.     I 742-1 786 

Rutherford  . 

1749-1819 

Lavoisier     . 

.     I 743-1 794 

Watt  . 

.     1736-1819 

Franklin 

.     1 706-1 790 

Galvani 

.     1 737-1 798 

Volta 

.     1 745-1827 

Maskelyne   . 

.     1732-1811 

Lagrange     . 

1736-1813 

Laplace 

1 749-1827 

Herschel 

.     1 738- 1 822 

CH.  XXIII.  DEVELOPMENT  OF  SCIENCE.  189 


CHAPTER  XXIII. 

SCIENCE   OF   THE   EIGHTEENTH    CENTURY. 

Great  spread  of  Science  in  the  Eighteenth  Century — Advance  of  the 
Sciences  relating  to  Living  Beings — Foundation  of  Leyden  Univer- 
sity in  1574 — Boerhaave,  Professor  of  Medicine  at  Leyden,  1701 — 
Foundation  of  Organic  Chemistry  by  Boerhaave — Influence  of  Boer- 
haave upon  tlie  study  of  Medicine — Belief  of  the  Alchemists  in 
*  Vital  Fluids ' — Boerhaave's  Experiments  on  the  Juices  of  Plants  — 
Dr.  Hales'  Experiments  on  Plants — Boerhaave's  Analyses  of  Milk, 
Blood,  &c. — Great  popularity  of  his  Chemical  Lectures. 

We  have  now  arrived  at  the  beginning  of  the  eighteenth 
century,  only  175  years  before  our  own  day,  when  the  dif- 
ferent sciences  which  we  have  been  tracing  in  their  rise,  Hke 
little  rills  on  the  mountain  sides,  were  beginning  to  swell 
out  into  mighty  streams,  widening  and  spreading  so  rapidly 
that  it  is  in  vain  we  strain  our  eyes  to  try  and  watch 
them  all.  The  time  had  now  come  when  any  man  who 
wished  to  be  a  discoverer  was  obliged  to  devote  his  whole 
life  to  one  branch  of  science,  following  it  out  in  all  its  in- 
tricate windings.  And  so  we  find  that  about  this  time  each 
science  begins  to  have  a  complete  history  of  its  own,  with 
its  own  eminent  men,  and  its  peculiar  language  growing 
more  and  more  technical  so  as  scarcely  to  be  understood  by 
ordinary  readers. 

For  this  reason  most  general  histories  of  Science  stop  at 
this  point  and  refer  their  readers  to  special  works  on  the 
different  sciences.     I  do  not,  however,  propose  to  do  this  ; 


I90  EIGHTEENTH  CENTURY.  pt.  hi. 

for  though  I  must  warn  you  again  more  strongly  than  ever 
that  I  can  only  give  you  little  glimpses  of  the  work  that  was 
being  done,  still  I  think  that  if  we  struggle  on  through  the 
increasing  mass  of  knowledge  and  gather  up  a  fragment  here 
and  there,  you  will  gain  a  general  idea  of  the  progress  of 
science,  and  be  able  to  read  more  advanced  scientific  books 
with  much  greater  interest,  even  though  you  may  have 
learnt  very  little  of  any  one  science. 

Astronomy,  Physics,  and  to  a  certain  extent  Chemistry, 
had  made  such  a  start  at  the  end  of  the  seventeenth  century 
that  it  was  a  great  many  years  before  those  men  who  came 
after  Newton,  Halley,  Huyghens,  and  Stahl,  had  mastered 
the  new  discoveries  sufficiently  to  progress  any  further. 
Therefore  we  find  that  it  was  not  in  these  sciences  that  most 
advance  was  made  in  the  beginning  of  the  eighteenth  cen- 
tury, but  in  those  which  relate  to  living  beings,  and  which 
are  all  included  under  the  head  of  Biology,  or  the  science  of 
life.  Medicine,  Anatomy,  and  Physiology  were  the  branches 
which  grew -most  rapidly  about  this  time  ;  and  the  five  great 
men  whose  names  stand  out  most  conspicuously  are  Boer- 
haave,  Haller,  John  Hunter,  Bonnet,  and  Spallanzani  : 
Boerhaave,  as  the  founder  of  the  study  of  organic  chemistry, 
Haller  and  Hunter  as  the  fathers  of  coinparative  anatomy, 
and  Bonnet  and  Spallanzani  as  the  discoverers  of  some  very 
remarkable  facts  m  physiology.  We  will  take  these  subjects 
in  regular  order,  and  try  to  understand  something  of  the 
work  which  was  done  in  them. 

Medical   School  of  Leyden Foundation  of  Organic 

Chemistry  by  Boerhaave,  1701. — On  the  coast  of  Holland, 
just  where  the  Rhine  empties  itself  by  a  number  of  small 
channels  into  the  German  Ocean,  stands  the  city  of  Leyden, 
which  became  famous  in  the   year  1574,  on  account  of  a 


CH.  XXIII.  HERMANN  BOERHAAVE.  191 

siege  of  four  months  which  the  starving  inhabitants  endured 
with  the  utmost  heroism,  when  the  Protestant  Netherlanders 
were  struggHng  for  Hfe  and  Hberty  against  PhiHp  II.  of  Spain. 
The  Dutchmen  were  successful  at  last  and  drove  out  the 
Spanish  army,  by  cutting  away  the  dykes  and  letting  the  sea 
swallow  up  their  beautiful  pastures,  their  neat  villages,  and 
their  fruitful  orchards  ;  and  as  a  reward  for  their  devotion  to 
the  cause,  William  of  Orange  founded  the  University  of 
Leyden,  which  afterwards  became  very  celebrated. 

Hermann  Boerhaave,  of  whose  work  we  are  now  going 
to  speak,  was  a  Professor  of  Medicine  in  this  University 
about  a  hundred  years  after  its  commencement.  The  son 
of  a  Dutch  clergyman,  he  was  born  in  1668  at  Vorhout,  one 
of  those  same  small  Dutch  villages  near  Leyden  which  had 
been  for  days  under  the  sea  in  1574.  His  father  intended 
him  for  the  church  ;  but  the  young  student,  having  been 
accused  of  holding  false  opinions,  was  only  too  glad  to  give 
up  this  profession  and  study  medicine,  in  which  he  de- 
lighted. He  was  so  successful  that  in  1701  he  was  made 
Lecturer  of  Medicine  in  the  University,  and  a  few  years 
later  the  Professorships  of  Chemistry  and  Botany  were 
also  given  to  him.  From  that  time  the  Medical  School  of 
Leyden  became  famous  all  over  the  world.  Students 
flocked  to  it  from  all  quarters,  and  most  of  the  best  me- 
dical men  of  Europe  were  pupils  of  Boerhaave.  This  was 
due  chiefly,  of  course,  to  his  wonderful  medical  knowledge 
and  his  skill  as  a  lecturer ;  but  his  popularity  was  greatly 
increased  by  his  enthusiasm,  kindly  temper,  and  the  great 
interest  which  he  took  in  the  success  of  his  pupils.  He 
was  always  ready  to  help  others  and  to  give  them  credit 
for  the  work  they  had  done,  and  it  is  said  that  even  his 
enemies  could   not  resist  his  constant  and   uniform  kind- 


192  EIGHTEENTH   CENTURY.  pt.  hi. 

ness  and  good-temper.  He  loved  his  science  too  well  to 
hinder  its  progress  by  angry  disputes ;  and  by  imparting 
this  spirit  to  his  pupils  he  did  almost  as  much  for  the 
spread  of  medical  science  as  by  the  facts  which  he  taught 
them. 

But  besides  his  influence  upon  medicine  in  general  there 
was  one  particular  study  which  Boerhaave  may  be  said  to 
have  founded  j  this  was  the  chemistry  of  living  substances, 
or  organic  chemistry.  You  will  remember  that  the  false 
science  of  alchemy  had  always  been  much  mixed  up  with 
chemistry,  and  the  alchemists  had  some  strange  mystical 
notions  about  *  vital  fluids/  which  they  supposed  to  exist  in 
animals  and  plants,  and  to  cause  their  life  and  growths  Little 
by  little,  however,  more  correct  ideas  had  grown  up  in  the 
1 6th  and  17th  centuries  about  the  nature  of  life.  Vesalius, 
Harvey,  Malpighi,  Grew,  and  many  others,  had  gradually 
described  more  and  more  accurately  the  working  of  the  dif- 
ferent organs  of  a  living  being,  and  now  Boerhaave  went 
farther,  and  tried  to  discover  by  means  of  chemistry  of  what 
materials  these  organs  themselves  are  composed. 

In  the  same  way  that  Geber  had  decomposed  or  divided 
up  inorganic  substances,  such  as  metals  and  earths,  by  distil- 
lation and  sublimation  (see  p.  44),  so  Boerhaave  proposed  to 
decompose  the  organic  substances  of  which  plants  and  ani- 
mals are  made,  and  to  discover  the  materials  contained  in 
them.  To  accomplish  this  he  took  a  plant,  such  as  rosemary, 
and  puttiiig  fresh  moist  leaves  of  it  into  a  furnace,  heated 
them  gently  and  drove  out  all  the  moisture,  which  he  col- 
lected in  a  separate  vessel.  When  this  moisture  had  cooled 
down  into  a  liquid  he  examined  it  and  found  that  it  was 
made  up  of  water,  and  of  different  kinds  of  oils  and 
essences,  according  to  the  plant  he  had  taken.  For  in- 
stance, from  rosemary  he  got  an  essence  with  the  peculiar 


CH.  XXIII.  ORGANIC   CHEMISTRY.  193 

scent  of  rosemary ;  from  the  bark  of  the  cinnamon  \xQQ,Laurus 
Camphorum,  or  Cinnamomum  camphoi'um^  he  got  essence  of 
cinnamon ;  from  its  roots,  camphor  ;  and  from  its  leaves  an 
oil  with  the  taste  of  cloves.  Then  after  he  had  extracted 
all  the  juice  from  the  plant,  he  burnt  the  dry  remains,  to  see 
what  would  be  contained  in  its  ashes  after  the  fire  had 
driven  off  part  of  the  solid  matter  as  gas,  and  he  found  in 
them  a  kind  of  salt,  which  was  also  different  in  different 
plants.  But  if  he  poured  hot  water  on  the  plant  before 
burning  it,  he  found  no  salt  in  the  ashes,  for  it  had  been 
dissolved  and  carried  off  in  the  water. 

Having  now  found  what  substances  were  in  the  plant, 
the  next  step  was  to  discover  where  they  came  from  ;  so  he 
took  several  specimens  of  earth  in  which  plants  can  grow 
and  examined  them  also  ;  and  he  found  that  he  could 
extract  from  them  many  of  the  substances,  such  as  salt, 
alum,  borax,  and  sulphur,  which  he  had  also  discovered  in 
the  ashes  of  the  plants.  It  was  clear,  then,  that  the  plant 
took  these  salts  out  of  the  earth ;  and  by  a  number  of  experi- 
ments he  went  on  to  prove  that  they  are  dissolved  by  the 
rain-water  which  sinks  into  the  earth,  and  are  then  sucked 
up  by  the  plants  through  their  roots  and  carried  up  to  the 
leaves,  where  they  are  exposed  to  the  air  and  sunshine,  and 
altered  so  as  to  become  food  for  the  plant  The  other 
parts  which  did  not  come  from  the  soil  he  concluded  must 
be  taken  in  from  the  air.  These  were  splendid  facts,  and 
curiously  enough  a  celebrated  English  chemist.  Dr.  Hales 
(born  1677,  died  1761),  made  some  of  the  same  experi- 
ments almost  at  the  same  time,  which  confirmed  those  of 
Boerhaave.  Hales  even  went  so  far  as  to  measure  the 
quantity  of  water  taken  in  at  the  roots  and  given  out  at 
the  leaves  of  plants,  and  he  discovered  the  way  in  which 
10 


194  EIGHTEENTH  CENTURY.  pt.  ill. 

plants  breathe  through  the  httle  stomata^  or  mouths,  disco- 
vered by  Grew  (see  p.  141). 

From  the  juices  of  plants  Boerhaave  next  went  on  to 
those  of  animals,  and  he  decomposed  in  a  most  beautiful 
and  simple  manner  milk,  blood,  bile,  and  those  fluids  called 
chyle  and  lymph  which  convey  nourishment  to  the  blood. 
These  he  compared  with  the  sap,  gums,  resins,  and  oils  of 
*  plants,  and  showed  that  animal  bodies  are  made  up  of 
altered  vegetable  matter,  just  as  plants  are  in  their  turn 
composed  of  ma<tter  taken  from  the  soil  and  the  air;  and 
he  suggested  that  by  careful  experiments  it  would  at  last  be 
possible  to  discover  exactly  the  materials  of  which  all  living 
beings  were  made. 

Boerhaave's  analyses  of  organic  substances  were  very 
rough  and  imperfect  compared  to  those  which  are  made  now; 
for  you  must  remember  that  the  four  gases,  oxygen,  hydro- 
gen, nitrogen,  and  carbonic  acid,  which  we  now  know  are  the 
chief  constituents  of  plants,  were  not  yet  discovered.  Yet 
even  these  rough  attempts  were  so  interesting  that  students 
crowded  round  the  doors  of  his  lecture-room  for  hours 
before  the  lecture  began,  to  secure  admission  ;  and  there  can 
be  no  doubt  that  his  '  Elements  of  Chemistry,'  published  in 
1732,  contained  the  first  steps  in  the  study  of  the  chemistry 
of  living  things.  Boerhaave  was  also  a  celebrated  botanist. 
He  died  in  1738,  and  deserves  always  to  be  remembered  as 
one  of  the  greatest  teachers  of  the  eighteenth  century. 


Chief  Works  consulted. — Brewster's  'Encyclopsedia ' — 'Boerhaave ;' 
Cuvier,  *  Hist,  des  Sciences  Naturelles  ; '  Sprengel,  '  Hist,  de  la  Medi- 
cine,' 181 5  ;  Burton's  *Life  and  Writings  of  Boerhaave,'  1746  ;  Boer- 
haave, 'Elements  of  Chemistry,' Englished  by  Dallo  we,  1735  ;  Miller's 
'Chemistry  ;'  Hales'  'Essays  concerning  Vegetable  Staticks,'  1759. 


CH.  XXIV.  HALLER— ANATOMIST.  195 


CHAPTER  XXIV. 

SCIENCE    OF   THE    EIGHTEENTH    CENTURY    (CONTINUED). 

Childhood  of  Haller — Foundation  of  the  University  of  Gottingen  in 
1736 — Haller  made  Professor  of  Anatomy — Haller's  Anatomical 
Plates — He  discovers  the  power  of  Contraction  of  the  Muscles — 
Rise  of  Comparative  Anatomy — ^John  Hunter's  industry  in  Dissect- 
ing and  comparing  the  Structures  of  different  Animals  —  His 
Museum  and  the  arrangement  of  his  Collection — Bonnet's  Experi- 
ments on  Plants  —  Experiments  upon  Animals  by  Bonnet  and 
Spallanzani — Regrowth  of  different  parts  when  cut  off — Bonnet's 
theory  of  Gradual  Development  of  Plants  and  Animals — Anatomical 
Works  of  Haller — He  discovers  the  power  of  the  Muscles  to  con- 
tract. 

Haller,  1708-1777.— Among  the  pupils  of  Boerhaave  there 
was  one  man  who  became,  if  possible,  even  more  famous 
than  his  master.  This  was  Albert  von  Haller,  son  of  the 
Chancellor  of  Baden,  who  was  born  at  Berne  in  1708,  and 
died  in  1777.  Haller  seems  to  have  been  a  most  extra- 
ordinary child  \  at  nine  years  of  age  it  is  said  that  he  knew 
Latin  and  Greek,  had  made  a  Hebrew  and  Greek  dictionary, 
a  Chaldean  grammar,  and  an  historical  dictionary  !  We 
are  not  told  how  good  these  books  were  ;  but  how  very  few 
boys  of  nine  years  old  would  have  been  able  to  write  them 
at  all !  At  seventeen  Hallef  went  to  Leyden  to  study  under 
Boerhaave,  and  under  Albinus,  a  famous  anatomist  j  and 
at  nineteen  he  was  already  a  doctor  of  medicine.  Having 
been  driven  out  of  Paris  because  the  people  were  horrified 


196  EIGHTEENTH   CENTURY.  pt.  hi. 

at  his  dissecting  dead  bodies,  he  went  to  Berne,  where  he 
became  professor  of  anatomy;  and  in  1736,  when  George 
II.  of  England,  who  was  also  Elector  of  Hanover,  founded 
the  University  of  Gottingen,  he  went  there  as  professor  of 
anatomy,  surgery,  and  botany,  and  soon  made  that  Univer- 
sity as  famous  as  Boerhaave  had  made  Leyden. 

One  of  his  first  reforms  was  to  turn  the  work  of  his  pupils 
to  good  account.  When  medical  students  are  going  to  pass 
their  last  examination  they  are  required  to  write  an  essay,  or 
thesis,  as  it  is  called,  before  they  can  receive  their  degree  of 
doctor.  Haller  used  always  at  these  times  to  propose  to 
each  one  of  his  students  some  difficult  point  in  anatomy  or 
physiology,  in  which  he  thought  new  discoveries  might  be 
made,  and  he  then  drew  out  a  plan  for  them  and  showed 
them  how  to  begin.  By  this  means  their  essays  were  often 
full  of  new  and  useful  information,  and  it  was  a  great  deal 
owing  to  the  help  of  his  pupils  that  Haller  was  able  to 
publish  180  volumes  on  science,  all  more  or  less  valuable. 

There  was  also  a  very  good  anatomical  theatre  at 
Gottingen,  and  from  dissections  made  there  Haller  produced 
a  set  of  most  beautiful  anatomical  drawings,  which  he  pub- 
lished between  1743  and  1753.  You  will  remember  that 
Vesalius  published  many  fine  engravings  of  parts  of  the 
human  body  (see  p.  67),  and  since  his  time  many  others 
had  been  made,  especially  by  Haller's  master,  Albinus.  But 
Vesalius'  drawings  were  coarse,  because  he  had  no  micro- 
scope to  help  him,  and  Albinus  had  only  drawn  separate 
parts,  such  as  a  muscle,  a  nerve,  or  a  vein.  Haller's  plates 
were  the  first  which  showed  the  different  nerves  and  vessels 
attached  in  their  right  position,  and  to  each  plate  he  added 
a  complete  history  of  the  function,  or  use  of  the  parts 
drawn.     He  made  these  drawings  so  accurate,  and  spent  so 


CH.  XXIV.  COMPARATIVE  ANATOMY.  197 

much  time  upon  each  minute  structure,  that  in  seventeen 
years,  with  all  the  help  he  had,  he  was  not  able  to  complete 
the  description  of  the  whole  human  body. 

Haller  discovers  the  Power  of  the  Muscles  to  Contract. 
— It  was  while  he  was  at  work  at  these  dissections  that  he 
made  one  great  discovery,  which  you  must  try  to  understand. 
If  you  clasp  your  right  hand  round  your  left  arm,  just  above 
the  elbow,  and  then  bend  your  left  arm,  you  will  feel  the 
part  under  your  hand  swell  up  and  grow  hard.  The  reason 
of  this  is  that  the  muscle  of  your  arm,  called  the  biceps,  has 
contracted,  or  grown  shorter  and  thicker,  in  the  process 
of  bending  your  arm.  If  you  open  your  arm  again,  the 
swelhng  will  go  down,  because  the  muscle  is  stretched  out. 
Now  before  Haller's  time  it  was  thought  that  the  muscles 
could  not  contract  of  themselves,  but  were  drawn  up  by  the 
nerves.  Haller  discovered  that  this  is  not  so,  but  that  a 
muscle,  if  irritated,  will  draw  itself  together  even  when  it  is 
quite  separated  from  the  nerves,  and  this  has  since  been 
proved  to  be  true  by  a  great  number  of  experiments.  So 
that  though  it  is  true  that  our  nerves  are  the  cause  of  our 
I  moving,  because  they  excite  the  muscles  and  so  make  them 
contract,  yet  the  real  power  of  contraction  is  in  the  muscle 
itself. 

Comparative  Anatomy,  or  the  Comparison  of  Different 
Structures  in  Men  and  Animals. — John  Hunter. — Another 
point  in  which  Haller  did  good  service  to  science  was  in 
comparing  the  same  parts  of  the  body  of  men  and  animals, 
and  showing  how  far  they  are  alike.  This  study,  which  is 
called  the  study  of  comparative  anatomy,  has  now  become 
very  important,  for  by  examining  any  organ,  such  as  the 
heart  for  example,  from  the  lower  animals  in  which  it  is 
very  simple,  up  to  man  in  whom  it  is  complicated,  we  can 


198  EIGHTEENTH  CENTURY.  pt.  hi. 

trace  its  gradual  improvement,  and  understand  it  much  more 
perfectly.  Aristotle  and  Vesalius  had  both  of  them  com- 
pared some  of  the  parts  of  different  animals,  and  so  had 
other  and  later  zoologists  ;  but  Haller  was  the  first  to  make 
it  a  regular  study,  and  John  Hunter,  who  lived  about  the 
same  time,  devoted  his  whole  life  to  it,  and  raised  it  to  the 
rank  of  a  separate  science. 

John  Hunter,  who  was  born  in  the  County  of  Lanark, 
in  1728,  was  the  brother  of  a  very  eminent  London  phy- 
sician, Dr.  William  Hunter,  who  was  also  a  great  anatomist. 
John,  being  delicate,  had  been  allowed  to  grow  up  with  very 
little  education,  and  at  twenty  years  of  age  he  came  up  to 
London,  a  mere  ignorant  lad,  to  try  and  help  his  brother  in  his 
anatomical  dissections.  Here  he  soon  showed  that  he  had 
plenty  of  ability,  for  he  learnt  dissecting  so  rapidly  that  at 
the  end  of  a  year  he  was  able  to  teach  his  brother's  pupils, 
and  before  long  he  became  one  of  the  leading  surgeons  at 
St.  George's  Hospital,  and  had  a  large  private  practice. 

But  though  he  made  a  great  deal  of  money  by  his  pro- 
fession, he  spent  it  all  upon  his  favourite  study  of  anatomy, 
to  which  he  devoted  every  spare  moment.  His  great  wish 
was  to  compare  thoroughly  the  different  parts  of  men  and 
animals,  so  as  to  show  how  the  life  of  each  one  of  them  is 
carried  on.  For  this  purpose  he  dissected  and  preserved  in 
different  ways  the  bodies  of  all  the  animals  he  could  lay  his 
hands  upon.  He  bought  up  all  the  wild  beasts  that  died  in 
the  Tower,  where  they  were  then  kept,  and  any  which  he 
could  procure  from  travelling  menageries,  and  he  even  kept 
foreign  animals  himself  in  a  piece  of  ground  at  Earl's  Court, 
Brompton,  that'he  might  watch  their  habits  and  dissect  their 
dead  bodies. 

As  years  went  on  and  his  specimens  increased  he  built  a 


CH.  XXIV.  HUNTER'S  MUSEUM.  199 

large  museum  in  Leicester  Square,  and  arranged  his  collec- 
tion so  as  to  show  which  parts  in  different  animals  serve  for 
the  sa.me  use.  For  example,  to  illustrate  the  way  in  which 
animals  digest  their  food,  he  placed  first  the  hydras,  polyps, 
and  sea-anemones,  which  are  all  stomach,  being  in  them- 
selves nothing  but  a  simple  bag  surrounded  by  little  feelers, 
and  having  a  fluid  inside  which  dissolves  the  food.  Then 
he  arranged  in  order  many  forms  up  to  the  leech,  which  is 
a  bag  with  two  openings,  and  has  a  head  and  nerves  and 
other  parts,  besides  a  stomach.  Then  came  the  insects, 
some  of  which,  as  the  bees,  have  a  separate  receptacle  for 
honey,  of  which  they  disgorge  a  part  and  then  pass  on  the 
rest  into  the  real  stomach.  Then  came  the  snails,  in  which 
the  stomach  is  a  separate  part  with  a  second  opening  to 
pass  out  the  food  it  cannot  take  up.  Then  the  fishes,  some  of 
whom  have  stomachs  strong  enough  to  crush  the  shells  and 
indigestible  parts  of  their  food,  while  others  have  the  mouth 
lined  with  teeth  for  this  purpose ;  then  came  the  stomachs 
of  reptiles ;  and  afterwards  those  of  birds,  with  the  curious 
crop  where  the  food  lies  first,  and  the  gizzard,  in  which  it  is 
rubbed  against  the  little  stones  which  the  bird  swallows. 
Then  finally  came  the  stomachs  of  the  higher  animals,  with 
many  curious  and  interesting  peculiarities ;  as  for  example, 
the  divided  stomach  of  those  animals,  such  as  the  calf,  which 
chew  the  cud,  and  of  the  camel,  in  which  one  division  serves 
as  a  water-bag.  And  side  by  side  with  these  organs  of 
digestion  he  placed  the  teeth  of  each  animal,  showing  how 
these  were  each  exactly  fitted  to  prepare  the  food  for  the 
particular  kind  of  stomach  of  the  animal  to  which  they 
belonged. 

In  this  way  Hunter  tried  to  arrange  the  history  of  all  the 
different  organs  of  the  body,  tracing  out  each  as  perfectly  as 


200  EIGHTEENTH  CENTURY.  pt.  hi. 

he  could,  and  showing  how  it  suited  the  wants  of  the  various 
animals.  His  museum  cost  him  an  immense  amount  of  labour, 
and  more  than  70,000/.  in  money ;  when  he  died,  in  1793,  it 
was  bought  by  the  English  Government  for  15,000/.  and 
placed  in  the  London  College  of  Surgeons,  and  for  the  last 
eighty  years  many  a  London  student  of  physiology  has  had 
occasion  to  be  thankful  to  the  rough  and  uneducated  John 
Hunter  for  the  laborious  and  careful  work  he  did,  and  the 
magnificent  collection  he  left  behind  him. 

Experiments  upon  Animals  by  Bonnet  and  Spallanzani. 
— ^While  Haller  and  Hunter  by  their  dissections  were  adding 
greatly  to  our  knowledge  of  the  structure  of  animals,  two 
famous  naturalists  in  Switzerland  and  Italy  were  bringing  to 
light  some  extremely  curious  and  interesting  facts  about  their 
growth. 

The  first  of  these,  named  Charles  Bonnet,  was  born  at 
Geneva  in  1720,  and  died  in  1793.  He  had  a  great  love  of 
natural  history,  and  when  he  was  twenty  years  of  age  he 
wrote  a  paper  upon  aphides^  or  plant-lice,  which  was  so  re- 
markable that  the  French  Academy  of  Sciences  at  once 
elected  him  one  of  their  corresponding  members.  He 
also  made  some  very  interesting  experiments  upon  plants, 
showing  that  they  have  the  power  of  seeking  out  for  them- 
selves what  is  necessary  for  their  growth.  We  all  know  that 
plants  grow  towards  the  light,  and  if  kept  in  a  dark  room 
will  seek  out  even  a  crack  through  which  the  light  comes. 
But  Bonnet  proved  that  they  will  do  much  more  than  this, 
for  he  found  that  if  he  twisted  the  branch  of  a  tree  so  as  to 
turn  the  leaves  bottom  upwards,  in  a  little  time  each  leaf 
turned  right  round  on  its  stalk  so  as  to  get  back  into  its 
natural  position  ;  while  on  the  other  hand,  if  he  hung  a  wet 
sponge  over  a  leaf,  the  leaf  would  turn  its  under  side  up- 


CH.  XXIV.  BONNET  AND  SPALLANZANI.  201 

wards,  so  as  to  bring  the  little  mouths,  or  stomata,  close  to 
the  sponge,  and  enable  them  to  drink  in  the  water.  In  this 
way  a  plant  will  always  find  out  the  best  way  of  growing  so 
as  to  get  as  much  sun  and  food  as  it  can.  Many  curious 
facts  of  this  kind  were  published  in  Bonnet's  work  on  the 
'  Use  of  the  Leaves  of  Plants,'  but  what  I  wish  now  particu- 
larly to  relate  to  you  are  his  experiments  upon  animals  and 
the  regrowth  of  limbs  which  had  been  cut  off. 

It  had  long  been  known  that  very  simple  organisms,  such 
as  polyps,  may  be  cut  in  pieces,  and  each  part  will  live  and 
become  a  perfect  creature ;  but  no  one  thought  it  possible 
that  any  of  the  more  complicated  living  beings  could  be 
treated  in  this  way.  Bonnet,  however,  and  the  famous 
Italian  naturalist  Spallanzani  (i 729-1 799)  proved  by  a  great 
number  of  experiments  that  tails,  legs,  and  even  heads  will 
grow  again  in  some  animals  after  they  have  been  cut  off. 
The  garden-worm,  for  example,  is  an  animal  with  many 
organs  :  it  has  numerous  bristles,  which  serve  as  feet,  it  has 
arteries  and  veins,  nerves,  and  organs  of  digestion,  and  a 
mouth  ;  yet  Bonnet  found  that  a  worm  if  cut  in  pieces  would 
grow  a  new  head  or  a  new  tail,  and,  what  was  still  more 
curious,  in  some  .rare  cases  it  grew  the  head  on  the  end  where 
the  tail  had  been  before  I 

Spallanzani  went  even  farther  than  this,  for  he  experi- 
mented on  snails.  Now  the  common  garden  snail  has  a 
head  with  four  horns,  moved  by  very  complicated  muscles, 
and  two  of  these  horns  have  eyes  at  the  end  of  them  j  more- 
over it  has  a  mouth,  with  teeth  and  a  tongue.  Spallanzani 
cut  off  first  the  horns  with  eyes,  and  afterwards  the  mouth 
and  tongue,  and  found  that  the  snail  had  power  to  re-grow 
them  all.  He  then  tried  upon  aquatic  salamanders,  which 
resemble  our  newts,  or  efts.     These  creatures  have  red  blood 


202  EIGHTEENTH  CENTURY.  pt.  hi. 

like  ourselves,  they  have  a  heart,  lungs,  bones,  and  muscles, 
and  their  legs  possess  muscles  and  nerves  like  those  of  a 
man  ;  yet  Spallanzani  cut  off  the  tail  and  legs  of  one  sala- 
mander six  times  in  succession,  and  in  another  case.  Bonnet 
cut  them  off  eight  times,  and  they  grew  again.  Bonnet  even 
took  out  the  right  eye  of  a  newt,  or  eft,  and  in  eight  months 
another  eye  had  grown  in  its  place.  These  experiments  were 
very  startling,  for  they  showed  that  the  life  of  the  lower 
animals  does  not  depend  on  a  particular  part  of  the  body  so 
much  as  it  does  in  ourselves  and  in  the  higher  animals.  If 
you  cut  off  the  head  of  a  man  or  an  ox,  they  die,  or  if  you 
cut  off  a  leg,  it  never  grows  again  ;  but  these  experiments 
proved  that  the  worm  and  the  snail  live  and  grow  new  heads 
and  limbs,  and  that  the  more  simple  an  animal  is,  the  more 
power  it  has  to  live  and  grow  after  it  is  cut  in  pieces. 

These  discoveries  led  Bonnet  to  make  a  suggestion  which 
I  want  you  to  remember,  because  we  shall  have  to  speak  of 
it  by-and-bye.  He  asked  whether  it  was  not  likely  that 
there  was  a  gradual  development  or  complication  of  the 
parts  of  the  body  as  you  ascend  from  the  lowest  plant  up  to 
the  highest  animal,  so  that  the  body  of  a  worm,  for  example, 
could  do  all  the  work  necessary  to  keep  it  alive  and  to  make 
it  grow,  without  the  help  of  its  head,  and  a  lizard  could  in 
the  same  way  make  a  new  leg  without  much  difficulty.  But 
as  the  machinery  grew  more  and  more  complicated  this  would 
not  be  so  easy,  till  at  last  it  would  become  impossible  in  the 
higher  animals,  just  as  in  a  complicated  machine  one  broken 
wheel  will  upset  the  whole  working.  Bonnet  wrote  a  book 
called  '  The  Contemplation  of  Nature,'  in  which  he  dwelt 
upon  this  subject,  and  tried  to  trace  out  how  animal  forms 
had  become  gradually  higher  and  higher,  till  they  had  arrived 
at  man.     We  shall  see  by-and-by  how  this  idea  occurred  also 


CH.  XXIV.         DEVELOPMENT  OF  ANIMALS.  203 

to  the  naturalist  Lamarck,  and  how  it  has  become  the  founda- 
tion of  a  grand  theory  of  Ufe  in  the  present  century.  Mean- 
while you  must  bear  in  mind  that  Bonnet  and  Spallanzani 
added  enormously  to  our  knowledge  of  the  lower  animals 
and  their  powers  of  life,  and  together  with  Boerhaave, 
Haller,  and  Hunter  did  a  great  deal  to  advance  the  sciences 
of  anatomy  and  physiology  in  the  beginning  of  the  eighteenth 
century. 


Chief  Works  consulted. — 'Life  of  Haller' — 'Naturalists'  Library;' 
Brewster's  'Encyclopaedia,'  arts.  'Physiology'  and  'Haller  ;'  Lawrence's 
'Lectures  on  Comparative  Anatomy,'  1816  and  1848;  Lawrence's 
translation  of  Blumenbach's  'System  of  Comparative  Anatomy,'  1807  ; 
*  Life  of  John  Hunter ' — '  Naturalists' Library,' vol.  x.  ;  Cuvier,  'Hist, 
des  Sciences  Naturelles  ;'  Carpenter's  '  Comparative  Physiology  ; '  Tom 
Taylor's  '  Leicester  Square,'  Appendix  by  Professor  Owen. 


204  EIGHTEENTH  CENTURY.  pt.  hi. 


'U 


HAPTER   XXV. 


Birth  a  )d  Early  Life  ot  Bulfon  and  Linnaeus  compared — BufFon's 
Work  Dn  ISaturai  History — Daubenton  wrote  the  Anatomical  Part 
— Buflbn's  Books  very  interesting,  but  not  always  accurate — He  first 
worked  out  tne  Distribution  of  Animals — Stniggles  of  Linnaeus 
with  Poverty  —  Mr.  Clifford  befriends  him — He  becomes  Professor  at 
Upsala — He  v«-as  the  first  to  give  Specific  Names  to  Animals  and 
Plants — Explanation  of  his  Descriptions  of  Plants  —  Use  of  the 
Linnasan  or  Artificial  System — Afterwards  superseded  by  the  Natural 
System — Linnaeus  fii'st  used  accurate  terms  in  describing  Plants 
and  Animals — Character  of  Linnaeus — Sale  of  his  Collection,  and 
Chase  by  the  Swedish  Man-of-war, 

Advance  of  Natural  History — Buffon  and  Linnaeus. — In 

the  year  1707  two  men  were  born,  the  one  in  France  and 
the  other  in  Sweden,  whose  names  have  become  almost 
equally  well-known,  although  they  were  by  no  means  equally 
great. 

The  Frenchman,  George-Louis  Le  Clerc  Buffon,  the  son 
of  a  counsellor  of  the  parliament  of  Dijon,  was  bom  on  his 
father's  estate  in  Burgundy.  The  Swede,  Karl  Linnaeus,  the 
grandson  of  a  peasant  and  son  of  a  poor  Swedish  clergy- 
man, was  born  in  a  small  village  called  Rashult,  in  the  south 
of  Sweden.  Buffon  enjoyed  the  best  education  which 
France  could  afford  him,  with  plenty  of  opportunity  to  culti- 
vate his  love  of  natural  history.  At  one-and-twenty  he 
succeeded  to  a  handsome  property,  and  after  travelling  foi 
some  time  settled  down  to  a  life  of  ease  and  Hterature,  partly 


CH.  XXV.  BUFFON'S  NATURAL   HISTORY.  205 

in  Paris,  and  partly  on  his  estate  in  Burgundy.  Linnaeus 
was  taught  in  a  small  grammar-school,  where  he  showed  so 
little  taste  for  books  that  his  father  would  have  apprenticed 
him  to  a  shoemaker  if  a  physician  named  Rothmann,  who  saw 
the  boy's  love  of  antural  history,  had  not  taken  him  into 
his  own  house  and  taught  him  botany  and  physiology.  At 
one-and-twenty,  when  Buifon  came  into  his  fortune,  the 
young  Linnaeus,  with  an  allowance  of  eight  pounds  a  year 
from  his  father,  was  a  struggling  student  at  the  University  of 
Upsala,  putting  folded  paper  into  the  soles  of  his  old  shoes 
to  keep  out  the  damp  and  cold. 

Buffon's  work  on  Natural  History :  he  traces  the 
Distribution  of  Animals. — Buffon's  private  life  is  not 
interesting.  He  was  a  vain  man,  and  not  a  moral  one  ;  but 
he  had  great  talents,  and  remarkable  perseverance  and 
industry.  In  1739  he  was  appointed  Superintendent  of  the 
Royal  Garden  and  Cabinet  at  Paris,  a  position  which  he 
held  till  his  death.  His  great  work,  of  which  we  must  now 
speak,  was  his  '  Natural  History,'  which  occupied  him  the 
greater  part  of  his  life.  It  is  one  comprehensive  history  of 
the  living  world,  containing  descriptions  of  all  the  animals 
then  known,  their  structure,  their  distribution,  their  habits, 
and  their  instincts,  and,  mingled  with  these,  many  curious 
theories  about  the  world  and  its  inhabitants. 

The  anatomical  part  of  this  work  was  done  by  a  physician 
named  Daubenton,  who  came  from  Buffon's  own  village,  and 
was  appointed  keeper  of  the  cabinet  of  natural  history 
through  his  influence.  Buffon  was  very  fortunate  in  having 
the  help  of  this  man,  for  having  weak  sight  himself,  and 
being  more  fond  of  general  theories  than  of  petty  details, 
this  part  of  his  work  would  have  been  very  poor  if  it  had 
not  been  for  Daubenton's  careful  and   conscientious   dis- 


2o6  EIGHTEENTH  CENTURY.  pt.  in. 

sections  and  descriptions.  The  rest  of  the  work  was  written 
chiefly  by  Buffon  himself,  who  bestowed  upon  it  immense 
pains  and  labour.  He  was  a  very  pleasing  writer,  and  did  a 
great  deal  for  natural  history  by  making  it  popular.  His 
books  were  more  like  romances  than  works  of  science,  but 
he  collected  in  them  a  great  deal  of  very  useful  information, 
and  put  it  in  a  shape  which  everyone  could  read  with 
pleasure,  and  in  this  way  led  people  to  think,  and  to  wish  to 
know  more  about  natural  history  and  the  habits  and  lives 
of  animals.  He  was  also  the  first  to  trace  out  with  any  care 
the  way  in  which  animals  are  distributed  over  different  parts 
of  the  globe;  how  they  are  checked  by  climate,  by 
mountains,  by  rivers,  and  by  seas  from  wandering  out  of 
their  own  regions,  and  how  they  are  more  widely  spread 
over  cold  countries  than  over  warm  ones,  because  they  are 
able  to  cross  the  seas  and  rivers  upon  solid  or  floating  ice, 
and  so  get  from  one  region  to  another. 

In  this  general  way  Buffon  gathered  together  a  great 
many  interesting  facts  about  animals.  His  works  were  all 
the  more  popular  because  he  disliked  anything  like  classi- 
fication. He  would  not  attempt  to  group  the  animals  after 
any  particular  method,  but  liked  to  describe  each  one  with 
a  little  history  of  its  own,  and  to  write  on  freely  without  any 
very  great  scientific  accuracy.  Of  course  the  consequence 
was  that  he  often  made  great  mistakes,  and  arrived  at  false 
conclusions ;  still  he  had  so  much  genius  and  knowledge 
that  a  great  part  of  his  work  will  always  remain  true,  and 
Natural  History  owes  a  great  deal  to  Buffon.  He  died  in 
1788,  in  the  eighty-first  year  of  his  age,  and  twenty  thousand 
people  assembled  to  do  him  honour  at  his  funeral. 

Life  and  Influence  of  linnseus,  1707-1778. — We  must 
now  turn  to  Linnaeus,  whose  whole  life  and  labours  were  as 


CH,  XXV.  EARLY  LIFE   OF  LJNNMUS,  207 

different  from  those  of  Buffon  as  his  birth  and  early  life  had 
been.  Buffon  hated  to  be  bound  down  to  exact  details ; 
Linnaeus  found  his  greatest  pleasure  in  tracing  out  each 
minute  character  in  plants  and  animals  so  accurately  as 
to  be  able  to  build  up  a  complete  classification,  by  which 
anyone  could  tell  at  once  to  what  part  of  the  animal  or 
vegetable  kingdom  any  living  being  belonged.  While  Buf- 
fon's  books  were  entertaining  and  readable,  Linnseus's  were 
often  hard  dry  science,  consisting  chiefly  of  long  accurate 
tables  and  minute  details  about  the  structure  of  animals  and 
plants.  Yet  Linnaeus's  writings  are  worth  infinitely  more 
than  those  of  Buffon's  for  one  simple  reason,  he  had  a  more 
earnest  love  of  t7'uth. 

Linnaeus  seems  to  have  been  bom  a  botanist.  He  writes 
in  his  own  diary  that  when  he  was  four  years  old  he  went  to 
a  garden  party  with  his  father  and  heard  the  guests  dis- 
cussing the  names  and  properties  of  plants ;  he  listened 
carefully  to  all  he  heard,  and  '  from  that  time  never  ceased 
harassing  his  father  about  the  name,  quality,  and  nature  of 
every  plant  he  met  with,'  so  that  his  father  was  sometimes 
quite  put  out  of  humour  by  the  incessant  questioning. 
However  at  last,  when  Dr.  Rothmann  took  him  into  his 
house,  he  had  opportunities  of  learning,  and  firom  that  time 
he  advanced  so  rapidly  that  he  was  soon  beyond  all  his 
teachers. 

In  1736,  after  meeting  with  many  kind  friends  in  his 
poverty,  and  making  a  journey  to  Lapland,  which  was  paid 
for  by  the  Stockholm  Academy  of  Science,  he  went  to 
Holland.  Here  he  called  on  the  celebrated  Boerhaave,  who 
with  his  usual  good  nature  introduced  him  to  a  rich  banker, 
named  Clifford,  who  was  also  a  great  botanist.  This  was 
the  turning-point  of  Linnaeus's  life.     Mr.   Clifford  invited 


2o8  EIGHTEENTH  CENTURY.  PT.  ill. 

him  to  live  with  him,  treated  him  Hke  a  son,  and  allowed 
him  to  make  free  use  of  his  magnificent  horticiilutral  garden. 
He  also  sent  him  to  England  to  procure  rare  plants,  and 
gave  him  a  liberal  income.  This  continued  for  some  time 
till  Linnseus's  health  began  to  fail,  and  he  found  besides 
that  he  had  learnt  all  he  could  in  this  place,  so  he  resolved 
to  leave  his  kind  friend  and  wander  farther.  Mr.  Clifford 
seems  to  have  been  much  hurt  at  his  leaving,  yet  he  con- 
tinued his  kindness  to  him  through  life. 

Linnaeus  went  to  Leyden  and  Paris,  and  from  there  to 
Stockholm,  where  he  practised  as  a  physician,  and  at  last  he 
settled  down  as  Professor  of  Medicine  and  Natural  History 
at  Upsala,  where  he  founded  a  splendid  botanical  garden, 
which  served  as  a  model  for  many  such  gardens  in  other 
countries,  such  as  the  Jardin  de  Trianon  in  France,  and 
Kew  Gardens  in  England.  His  struggles  with  poverty  were 
now  over  for  ever,  and  his  fame  as  a  botanist  was  spread  all 
over  the  world.  He  used  to  set  out  in  the  summer  days 
with  more  than  200  pupils  to  collect  plants  and  insects  in 
the  surrounding  country,  and  many  celebrated  people  came 
to  Stockholm  to  attend  Linnseus's  '  Excursions.'  Then  as  his 
pupils  spread  over  the  world  he  employed  them  to  collect 
specimens  of  plants  and  animals  from  distant  countries,  and 
he  himself  worked  incessantly  to  classify  them  into  one 
great  system. 

Liimseus  gives  Specific  Names  to  Plants  and  Animals. 
— And  now  we  must  try  to  seize  upon  the  chief  points  of 
Linnseus's  work,  that  you  may  be  able  to  understand  some- 
thing of  what  he  did  for  science,  although  it  is  quite  impos- 
sible for  us  to  give  even  a  sketch  of  his  divisions  of  the 
animal  and  vegetable  kingdoms.  The  first  and  greatest 
point  of  all  was  that  he  gave  a  second  or  specific  name  to 
every   plant  and  animal.      Before   his   time   botanists  had 


cii.  XXV.  LINN^US  ON  SPECIES.  209 

only  given  one  name  to  a  set  of  plants  ;  calling  all  roses,  for 
example,  by  the  name  Rosa,  and  then  adding  a  descrip- 
tion to  show  which  particular  kind  of  rose  was  meant. 
Thus,  for  instance,  for  the  Dog-rose  they  were  obliged  to 
say  Rosa,  sylvestris  vulgaris,  flore  odorato  incarnato,  that  is, 
'common  rose  of  the  woods  with  a  flesh-coloured  sweet- 
scented  flower.'  This,  you  will  see,  was  extremely  incon- 
venient ;  it  was  as  if  all  the  children  in  a  family  were  called 
only  by  their  father's  name,  and  you  were  obliged  to  describe 
each  particular  child  every  time  you  mentioned  him  ;  as 
'  Smith  with  the  dark  hair,'  or  '  Smith  with  the  long  nose  and 
short  fingers,'  &c.  A  botanist  named  Rivinus  had  suggested 
in  1690  that  two  names  should  be  given  to  plants,  and 
Linnaeus  was  the  first  to  act  upon  this  idea  and  to  give  a 
second  specific,  or,  as  he  called  it,  trivial  name  to  each  par- 
ticular kind  of  plant,  describing  the  plant  at  the  same 
time  so  accurately  that  anyone  who  found  it  could  decide  at 
once  to  what  species  it  belonged.  To  accomplish  this  he 
classified  all  plants,  chiefly  according  to  the  number  and 
arrangement  of  their  stamens  and  pistils  (or  those  parts 
which  produce  the  seeds),  and  then  he  subdivided  them 
by  the  character  and  position  of  their  leaves  and  other  parts. 
In  describing  the  geranium,  for  example,  he  mentions 
first  the  '  sepals,'  or  little  green  leaves  under  the  flower ;  he 
says  they  are  five,  and  very  pointed  ;  then  the  '  petals,'  or 
flower-leaves,  are  five  also,  growing  on  the  sepals  and 
heart-shaped  ;  the  *  stamens  '  are  ten  in  number,  and  grow 
separate  ;  the  little  vessels  on  the  top  of  the  stamens,  which 
are  called  *  anthers,'  and  hold  the  yellow  dust,  are  oblong  ; 
the  'pistil,'  or  seed-vessel,  is  formed  of  five  parts,  which 
are  joined  together  into  one  long  beak  which  ends  in  five 
points  j  the  seeds  are  covered  with  a  skin  and  are  shaped 


2IO  EIGHTEENTH   CENTURY.  pt.  hi. 

like  a  kidney,  having  often  a  long  tip  which  is  rolled  round 
in  a  spiral  (like  a  corkscrew).  Here  we  have  a  definition 
of  the  ge?ius  geranium  \  but  many  geraniums  will  answer  to 
this  description,  so  he  goes  on  to  describe  some  more 
special  characters.  The  sepals  in  this  particular  specimen, 
he  says,  are  joined  together  in  one  piece  \  the  stem  of  the 
plant  is  woody,  the  joints  are  fleshy,  the  leaves  are  slightly 
feathered  at  the  edge.  These  last  characters  are  peculiar  to 
this  kind  of  geranium,  which  he  calls  .Geraniu7n  gibbosum, 
and  here  we  have  the  specific  name.  Any  geranium  which 
has  the  woody  stem,  the  joined  sepals,  the  fleshy  joints, 
and  the  feathery-edged  leaves,  will  be  the  species  called  by 
Linnaeus  gibhosMin. 

You  will  see  that  by  this  system  it  is  always  possible  to 
find  out  easily  to  what  part  of  the  vegetable  kingdom  your 
plant  belongs  and  what  its  name  is ;  and  if,  after  you  have 
traced  its  genus,  there  is  no  species  which  exactly  agrees 
with  yours,  you  then  know  that  you  have  discovered  a  new 
species  which  has  not  been  described  before.  Linnaeus 
classified  animals  after  this  same  plan,  quadrupeds  chiefly  by 
their  teeth,  and  birds  by  their  beaks,  and  after  his  system 
was  complete  anyone  could  discover  the  scientific  name  of  a 
plant  or  animal  by  exercising  a  little  care  and  patience. 
This  system  is  called  the  Linnaean,  or  artificial  system^  be- 
cause it  only  selects  a  few  particular  parts  of  a  plant,  so 
as  to  help  you  to  look  it  out  in  a  kind  of  dictionary.  It  tells 
you  very  little  of  the  real  or  natural  life  of  the  plant,  and 
often  brings  some  very  near  together  which  are  really  very 
different.  It  is  as  if  you  classified  people  by  some  par- 
ticular feature,  such  as  those  who  had  long  hair,  or  short 
hair,  dark  or  light,  curly  or  straight.  This  might  be  very 
useful  for  recognising  them,  but  it  would  be  quite  artificial. 


CH.  XXV.  LINN^AN  SYSTEM.  211 

and  would  tell  you  very  little  about  their  real  relationship. 
Therefore  this  classification  has  now  been  partly  set  aside 
for  another  or  natural  classification,  which  Linnaeus  also 
suggested,  only  he  thought  it  too  difficult  for  ordinary  people ; 
and  which  was  worked  out  by  a  French  botanist  named 
Jussieu,  as  we  shall  see  by-and-by.  But  the  Linnsean 
system  is  still  extremely  useful  for  finding  the  name  of  a 
plant  or  animal,  and  many  people  in  the  last  century  were 
led  to  study  zoology  and  botany  by  the  simplicity  of  the 
classifications  of  Linnaeus. 

The  other  useful  point  in  Linnaeus's  system  was  the 
accurate  and  precise  terms  he  invented  for  describing  plants. 
Before  his  time  naturalists  used  any  words  which  suited 
them,  and  as  different  people  have  often  very  different  ideas 
as  to  what  is  meant  by  long  or  short,  round  or  pointed,  &c., 
the  descriptions  were  often  of  very  little  value.  ,  But 
Linnaeus  could  not  work  out  his  system  without  using  very 
clear  terms  and  explaining  beforehand  what  he  meant  by 
them  ;  and  as  his  nomenclature,  or  system  of  names,  was  soon 
followed  in  other  countries,  botanists  in  all  parts  of  the 
world  were  able  to  recognise  at  once  what  was  meant  by  the 
description  of  any  particular  plant.  The  same  advantage 
arose  out  of  his  classification  of  animals,  and  the  care  with 
which  he  traced  out  their  chief  characters.  I  wish  I  could 
have  given  you  some  idea  of  this  system,  which  was  fully 
explained  in  the  '  Systema  Naturae,'  completed  in  1768.  But 
when  you  remember  that  Linnaeus  classified  minutely  the 
whole  of  the  animals  and  plants  known  in  the  world,  you 
will  perceive  that  I  should  have  to  write  a  separate  book  to 
make  you  understand  it.  If  you  can  only  remember  that  he 
did  build  up  this  artificial  system,  and  that  he  was  the  first  to 
give  specific  names  to  plants  and  animals  and  to  create  an 


212  EIGHTEENTH  CENTURY.  pt.  hi. 

accurate  nomenclature  all  over  the  world,  you  will,  I  think, 
have  learnt  as  much  as  you  need  at  present  about  the  work 
of  the  great  Swedish  naturalist. 

Linnaeus  was  not  a  vigorous  old  man.  The  hard 
struggles  of  his  youth  and  the  immense  work  of  his  after- 
life had  worn  him  out,  and  at  fifty-six  he  was  obliged  to  ask 
the  King  of  Sweden  to  let  his  son  lecture  sometimes  in  his 
place.  AVith  this  help  he  continued  to  work  at  science  till 
within  two  years  of  his  death,  when  his  mind  became  feeble. 
He  died  in  1778,  loaded  with  honours  and  beloved  and 
esteemed  by  the  greatest  men  all  over  the  world.  His  had 
been  a  noble  life  \  enthusiastic  and  truth-loving,  he  had 
worked,  even  when  he  was  poor,  for  science  and  not  for 
wealth,  and  when  he  became  famous  and  rich  he  helped  his 
pupils  as  others  had  helped  him,  and  lived  simply  and 
frugally  till  his  death.  Unlike  Buffon,  his  private  life  was  as 
pure  as  his  public  life  was  famous.  Over  the  door  of  his 
room  he  placed  the  words  ^  Innocue  vivito,  Numen  adest^ 
('  Live  innocently,  God  is  present '),  and  he  lived  up  to  his 
motto.  His  study  of  nature  had  filled  him  with  deep 
reverence  and  love  for  the  Great  Creator,  and  he  used  often 
to  tell  his  friends  how  grateful  he  was  to  God  for  those  gifts 
which  had  made  his  life  so  full  of  interest  and  delight. 

After  the  death  of  Linnaeus  his  mother  and  sisters  sold 
his  collection  of  plants  and  insects,  and  all  his  books  and 
manuscripts,  to  Dr.  Edward  Smith  (afterwards  Sir  E.  Smith), 
for  one  thousand  pounds.  The  King  of  Sweden  was  at  this 
time  away  from  Stockholm,  but  directly  he  returned  and 
heard  that  such  a  valuable  national  treasure  was  on  its  way 
to  England  he  sent  a  man-of-war  to  try  and  bring  it  back. 
A  very  amusing  chase  then  took  place  ;  Dr.  Smith  did  not 
mean  to  lose  his  prize  if  he  could  help  it,  so  he  set  full  sail 


CH.  XXV.  LINNAiAN  COLLECTION.  213 

and  literally  ran  away  till  he  reached  the  Thames,  and 
landed  safely  in  London  without  being  caught.  Thus  the 
Linnsean  collection  came  to  England,  and  is  now  in  Bur- 
lington House.  The  Swedes  are  naturally  sorry  that  it  left 
their  country,  but  on  the  other  hand  it  has  become  more 
known  to  scientific  men  in  London  than  it  could  ever  have 
been  in  Stockholm.  With  Linnaeus  we  must  end  for  the 
present  the  history  of  the  sciences  relating  to  living  beings. 
Early  in  the  nineteenth  century  we  shall  return  to  them 
again,  but  in  the  next  chapter  we  must  learn  something  of  a 
new  science  which  arose  about  this  time ;  namely,  the 
science  of  '  Geology,'  or  the  study  of  the  earth. 


Chief  Works  consulted. — ^Jardine's  '  Naturalists'  Library,'  vols.  ii.  and 
xiii.  ;  Brewster's  *  Encyclopaedia ' — '  BufFon  and  Linnseus  ; '  Cuvier, 
*  Histoire  des  Sciences  Naturelles;'  Smith,  Sir  J.,  'Introduction  to 
Botany ; '  Pulteney's  '  View  of  Writings  of  Linnseus  j  *  Linnaeus, 
'  Systema  Naturae. ' 


214  EIGHTEENTH  CENTURY.  pt.  hi. 


CHAPTER  XXVI. 

SCIENCE    OF   THE   EIGHTEENTH    CENTURY   (CONTINUED). 

The  Study  of  the  Earth  neglected  during  the  Dark  Ages — Prejudices 
concerning  the  Creation  of  the  World — Attempts  to  Account  for 
Buried  Fossils — Palissy,  the  Potter,  first  asserted  that  Fossil-shells 
are  real  Shells — Scilla's  Work  on  the  Shells  of  Calabria,  1670 — 
Woodward's  Description  of  Different  Formations,  1695 — Lazzaro 
Moro  one  of  the  first  to  give  a  true  explanation  of  the  facts — Abra- 
ham Werner  lectures  on  Mineralogy  and  Geology,  1775 — Disputes 
between  the  Neptunists  and  Vulcanists — Dr.  Hutton  first  teaches 
that  it  is  by  the  Study  of  the  Present  that  we  can  understand  the 
Past — Theory  of  Hutton — Sir  J.  Hall's  Experiments  upon  Melted 
Rocks — Hutton  discovers  Granite  Veins  in  Glen  Tilt — William 
Smith,  the  *  Father  of  English  Geologists ' — His  Geological  Map  of 
England. 

Early  Prejudices  concerning  the  Formation  of  the 
Rocks. — You  will  no  doubt  remember  that  when  we  were 
speaking  of  the  science  of  the  Greeks,  we  learnt  (p.  11)  that 
Pythagoras  made  many  interesting  observations  about  the 
crust  of  the  earth,  which  led  him  to  say  that  the  sea  and 
land  must  have  changed  places  more  than  once  since  the 
creation  of  the  world.  Especially  he  pointed  out  that  sea- 
shells  are  found  inland;  deeply  buried  in  the  hills  ;  and  that 
the  sea  eats  away  land  on  the  coast  in  some  places,  while  in 
others  earth  is  washed  down  by  the  rivers  and  laid  at  the 
bottom  of  the  ocean. 

We  have  now  passed  over  more  than  2,000  years  since 
the  time  of  Pythagoras,  and  you  will  notice  that  we  have 


CH.  XXVI  GEOLOGY  215 

heard  nothing  more  about  observations  of  this  kind.  The 
fact  is,  that  during  the  Dark  Ages  the  study  of  the  earth  had 
been  ahnost  entirely  neglected,  and  people  had  taken  up  the 
mistaken  notion  that  they  ought  to  believe,  as  a  matter  of 
faith,  that  the  world  was  created  in  the  beginning  just  as  we 
now  see  it.  But  knowledge  and  inquiry  were  advancing  so 
fast  in  the  eighteenth  century,  that  it  was  impossible  for  such 
ignorance  to  continue  long.  People  could  not  go  on  digging 
wells  and  making  mines  in  all  parts  of  the  world  without 
being  struck  by  the  way  in  which  the  different  strata^  or 
layers  of  rock,  are  arranged  in  the  earth's  crust,  nor  without 
noticing  the  fossil  shells,  plants,  and  bones  of  animals  which 
they  found  buried  at  great  depths. 

At  first  they  were  very  unwilling  to  believe  that  these 
remains  had  ever  belonged  to  living  animals  and  plants,  and 
they  tried  to  imagine  that  they  v/ere  only  stones  resembling 
shells,  leaves,  &c.,  which  had  been  in  some  way  mysteriously 
created  in  the  earth.  Then,  when  this  absurd  idea  was 
given  up,  they  next  enquired  whether  a  universal  flood 
might  not  have  spread  them  over  the  land  ;  but  though  this 
opinion  was  upheld  for  more  than  a  hundred  years,  yet  it 
Avas  clear  to  all  those  who  really  studied  the  subject  that  it 
could  not  account  for  the  many  layers  of  fossils  deeply 
buried  in  the  earth. 

First  Attempts  to  study  the  Fossil  Remains  and  the 
beds  containing  them. — At  last,  little  by  little,  there  arose 
men  who  adopted  the  more  sensible  plan  of  studying  the 
different  formations  in  the  crust  of  the  earth  before  making 
theories  about  them.  Bernard  de  Palissy,  the  maker  of  the 
famous  French  pottery,  was  the  first  to  assert,  in  1580,  that 
the  fossil  shells  were  real  sea-shells  left  by  the  waters  of  the 
ocean;  then,  in  1669,  we  find  Steno,  a  Dane,  writing  a  re- 


2i6  EIGHTEENTH  CENTURY.  pt.  hi. 

markable  work  on  petrifactions  in  the  rocks;  and  in  1670 
Scilla,  an  Italian  painter,  published  a  treatise  on  the  fossil 
shells  and  other  remains  in  the  rocks  of  Calabria,  and  made 
some  beautiful  drawings  of  these  remains,  which  may  now 
be  seen  in  the  Woodwardian  Museum  at  Cambridge.  Next 
we  find  our  own  scientific  men,  Hooke,  the  naturalist  Ray, 
and  a  famous  geologist  Dr.  Woodward,  speculating  why  the 
earth's  crust  is  made  up  of  different  layers,  one  above 
another,  with  different  fossils  in  each.  Woodward  (1695) 
made  a  careful  collection  of  specimens  of  chalk,  gravel,  coal, 
marble,  and  other  rocks,  together  with  the  fossils  which  he 
found  in  them  ;  and  these  also  are  in  the  Cambridge  Mu- 
seum. But  all  these  men,  though  they  did  good  work,  still 
held  very  erroneous  notions  about  the  way  in  which  the 
crust  of  the  earth  had  been  formed. 

The  first  geologist  who  gave  any  real  explanation  of  the 
facts  was  Lazzaro  Moro,  an  Italian,  born  at  Friuli  in  Lom- 
bardy,  in  1687.  Moro  pointed  out,  as  Woodward  had  done 
before  him,  that  the  different  strata  lie  in  a  certain  order  one 
above  the  other,  and  that  within  them  are  imprisoned  fossil 
fishes,  shells,  corals,  and  plants,  in  all  countries,  and  at  all 
heights  above  the  sea.  The  rocks,  said  Moro,  writing  in 
1740,  must  have  been  soft  when  these  fossils  were  buried  in 
them,  and  some  must  have  been  near  rivers,  because  they  con- 
tain fresh-water  animals  and  plants  j  while  others  contain  only 
marine  fossils,  and  must  have  been  laid  down  under  the  sea. 
It  is  clear,  then,  that  they  must  all  have  been  formed  in  lakes 
or  seas,  and  have  been  raised  up  by  earthquakes,  or  thrown 
out  by  volcanoes,  such  as  we  see  taking  place  from  time  to 
time  in  the  world  now.  This  explanation,  though  rough,  was 
true,  and  Moro  deserves  to  be  remembered  as  one  of  the 
first  men  who  led  the  way  towards  a  true  study  of  the  earth. 


CH.  XXVI.  WERNER   ON  GEOLOGY.  217 

After  him  there  followed  many  others,  whom  we  cannot 
mention  here;  but  the  next  whose  name  is  famous  was 
the  great  Werner,  professor  of  mineralogy  at  Freyberg  in 
Saxony. 

Werner  calls  Attention  to  Geology,  1775. — Abraham 
Werner,  the  son  of  an  inspector  of  mines  in  Silesia,  was 
born  in  1750.  His  first  playthings  were  the  bright  minerals 
which  his  father's  workmen  gave  him,  so  that  he  knew  them 
by  sight,  even  before  he  could  tell  their  names ;  and  as  he 
grew  up  he  seemed  to  care  for  nothing  but  mineralogy  and 
the  wonderful  facts  it  revealed  about  the  formation  of  the 
earth.  Freyberg,  when  he  first  began  to  lecture  there,  in 
1775,  was  only  a  small  school  for  miners ;  but  it  was  not  long 
before  he  raised  it  to  the  rank  of  a  university,  so  great  was 
the  fame  of  his  lectures.  He  pointed  out  to  those  who  came 
to  learn  of  him,  that  the  study  of  the  rocks  was  something 
more  than  merely  searching  for  minerals  ;  and  that  the  crust 
of  the  earth  was  full  of  wonderful  histories,  which  might  be 
read  by  those  who  cared  to  take  the  trouble.  He  pointed 
out  how  some  formations  were  stratified,  that  is,  arranged  in 
layers,  and  contained  fossil  shells  and  other  organic  remains  ; 
while,  on  the  other  hand,  some  were  unstratified,  and  had 
no  fossils  in  them.     Some  rocks  were  bent,  as  in  Fig.  35 ; 

Fig.  35.  .     , 


Diagram  of  Bent  Rocks.    (Page.) 

Others  had  been  snapped  asunder  and  forced  one  up  and 
the  other  down,  as  in  Fig.  36  ;  and  he  bade  them  try  to  seek 
out  the  reason  of  these  bendings  and  breakings  of  the  earth's 
crust.  He  reminded-  them  also  that  mining  was  one  of  the 
11 


2i8  EIGHTEENTH  CENTURY.  pt.  hi. 

great  roads  to  wealth,  and  that  even  the  history  of  nations 
often  depended  upon  the  kind  of  ground  which  they  had 
under  their  feet.  By  facts  such  as  these  he  opened  men's 
eyes  to  see  the  wonders  of  the  earth's  crust,  so  that  people 
began  to  talk  everywhere  of  the  geological  lectures  of  Werner, 
and  numbers  flocked  from  distant  countries,  and  even  learnt 
the  German  language,  that  they  might  come  and  hear  him. 

In  this  way  he  spread  the  love  of  geology  all  over  Eu- 
rope. He  was  so  eager  and  earnest  himself  that  his  pupils 
could  not  fail  to  catch  some  of  his  enthusiasm,  and  to  try  to 
follow  out  his  ideas.      But,  unfortunately,  this  very  enthu- 


Diagram  of  rocks  which  have  been  rent  apart  at  the  pointy)  and  tilted  up,    i,  i,  2,  2, 
&c.,  Beds  which  before  the  distuibance  were  continuous.' 

siasm  led  him  to  insist  upon  a  theory  which  kept  back  his 
favourite  science  for  many  years. 

Neptunists  and  Vulcanists. — Werner  had  only  studied  a 
small  part  of  Germany,  and  there  were  then  very  few  de- 
scriptions of  other  parts  of  the  world  which  he  could  read ; 
and  so,  from  want  of  knowledge,  he  formed  the  mistaken 
idea  that  in  olden  times,  after  the  globe  had  cooled  down 
and  become  fit  for  living  beings,  there  were  no  volcanoes 
for  long  ages,  but  that  basalt  and  other  rocks,  which  we 
now  know  were  made  by  volcanic  heat,  were  all  laid  down 
by  water.  There  were  men  living  in  Werner's  time  who 
knew  that  this  was  a  wrong  theory,  but  he  would  not  listen 
to  their  arguments,  and  the  two  parties  became  so  violent 
that  many  years  were  lost  in  angry  disputes  between  the 

'  Kindly  drawn  for  me  by  Professor  Ramsay. 


CH.  XXVI.  BUTTON  ON  GEOLOGY,  219 

Neptunisfs,  or  those  who  thought  all  rocks  were  laid  down 
by  water,  and  the  Viikanists^  who  contended  that  many  rocks, 
such  as  basalt,  were  made  by  volcanic  heat. 

Hutton  teaches  that  it  is  by  the  Study  of  Changes 
going  on  now  that  we  can  alone  learn  the  History  of  the 
Fast. — While  these  discussions  were  going  on  upon  the 
Continent,  a  Scotchman  was  setting  to  work  in  the  right 
way  to  settle  the  question.  This  man  was  Dr.  Hutton, 
one  of  the  greatest  geologists  that  has  ever  lived ;  and  the 
reason  of  his  greatness  was  the  same  which  we  have  found  at 
every  step  in  our  history  of  science.  Before  he  made  any 
theory  he  sought  out  the  facts.  He  travelled  and  observed 
for  himself,  he  collected  patiently  details  about  the  layers  or 
strata  in  the  formations  of  all  countries  through  which  he 
passed  \  and  it  was  only  after  all  these  investigations  that  in 
1788,  when  he  was  sixty  years  of  age,  he  wrote  his  famous 
'  Theory  of  the  Earth,'  in  which  he  showed  how  the  history 
of  the  earth's  crust  might  be  traced  out  This  work,  al- 
though very  interesting,  was  not  much  read ;  but  one  of 
Hutton's  favourite  pupils,  the  celebrated  Dr.  Playfair,  wrote 
a  book  called  '  Illustrations  of  the  Huttonian  Theory,'  by 
means  of  which  Hutton's  opinions  became  well  known. 

About  Hutton  himself  there  is  very  little  to  tell.  He  was 
born  in  Edinburgh  in  1726,  studied  medicine,  and  took  his 
doctor's  degree  in  Leyden  in  1749,  and  then  returned  to 
Edinburgh,  and  devoted  all  his  life  to  science.  Of  his 
teaching  I  should  like  to  write  a  great  deal,  but  we  must 
content  ourselves  with  a  little  which  you  can  understand. 
His  great  principle  was  that  it  was  useless  to  try  and  guess 
how  the  rocks  had  been  made  and  fossils  buried  in  them, 
for  this  had  only  led  to  endless  confusion  and  disputes. 
Men  must  go,  he  said,  and  see  with  their  own  eyes  how 


220  EIGHTEENTH  CENTURY.  pt.  hi. 

rocks  are  being  made  now,  how  rivers  and  glaciers  are 
carrying  down  earth  and  stones  from  the  mountains  into  the 
sea,  and  how  volcanoes  are  throwing  out  melted  matter 
which  cools  dowTi  into  hard  rock  j  and  then  they  must  com- 
pare these  with  the  older  rocks  in  the  crust  of  the  earth,  and 
see  whether  they  were  not  formed  in  the  same  way. 

Aqueous  (or  water-made)  Rocks. — When  we  find  a  piece 
of  marble  made  up  almost  entirely  of  oyster  and  other  shells, 
and  of  pieces  of  coral,  we  cannot  doubt  that  it  must  once  " 
have  been  a  heap  of  loose  shells  and  corals  such  as  we  now 
see  on  the  shore  or  under  the  water,  and  that  it  has  since 
been  hardened  into  Hmestone.  When  we  find  that  by 
crushing  or  scraping  sandstone  we  can  turn  it  into  sand 
like  that  which  we  see  on  the  seashore,  and  which  we  know 
has  been  made  by  the  sea  grinding  the  stones  and  rocks  of 
the  beach  against  each  other,  then  we  cannot  doubt  that 
the  sandstone  has  once  been  loose  sand,  and  before  that  was 
part  of  a  rock  which  has  been  ground  down  by  the  waves. 

And  so  we  are  led  to  the  conclusion  that  the  rocks  of 
our  earth,  as  we  see  them  now,  have  been  formed  out  of  the 
materials  of  still  older  rocks  which  existed  before  them,  and 
are  being  gradually  moulded  into  other  and  newer  rocks, 
which  will  exist  when  these  have  been  destroyed.  Our  solid 
earth  is  being  wasted  every  day.  The  sides  of  the  moun- 
tains are  washed  down  and  their  materials  are  carried  through 
the  valleys  by  the  running  water.  In  this  way  the  soil  is 
brought  down  to  the  coast,  and  here  it  is  eaten  away  by  the 
waves  of  the  sea,  and  falls  to  the  bottom  of  the  ocean,  out 
of  which  it  will  be  raised  again  by  earthquakes,  volcanoes, 
and  other  movements  of  the  earth's  crust,  such  as  can  be 
proved  to  be  going  on  in  parts  of  the  world  at  this  day.  As 
far  back  as  investigations  and  reasoning  can  go  we  find 


CH.  XXVI.  IGNEOUS  ROCKS.  221 

everywhere  signs  that  these  gradual  and  incessant  changes 
have  always  been  going  on,  and  that  the  face  of  our  earth, 
as  we  now  see  it,  has  been  moulded  out  of  the  ruins  of  an 
older  world. 

Igneous  (or  fire-made  Eocks). — But  how  are  we  to  decide 
about  those  rocks,  such  as  basalt,  which  Werner  thought 
were  made  by  water?  Hutton  was  convinced  they  were 
formed  in  volcanoes  ;  and  yet  it  was  true  that  they  did  not 
contain  bubbles  of  air  as  lava  does,  which  has  poured 
down  the  sides  of  a  volcano  in  the  open  air.  Here  his 
friend  and  pupil  Sir  James  Hall  came  to  his  assistance  by 
melting  pieces  of  rock  in  his  chemical  laboratory,  and  letting 
them  cool  do\^n  under  very  heavy  pressure.  When  this  was 
done  they  could  hardly  be  distinguished  from  pieces  of 
basalt  which  he  took  out  of  the  earth.  It  is  clear,  there- 
fore, he  said,  that  these  rocks  have  either  cooled  down  in- 
side the  volcano,  with  a  great  weight  of  rocks  above  them, 
or  have  been  poured  out  under  the  sea,  which  would  press 
down  heavily  upon  them  and  shut  out  the  air. 

Another  question  which  Hutton  cleared  up  in  the  same 
way  was  that  of  the  formation  of  granite.  Werner  believed 
that  all  the  granite  rocks,  of  which  you  may  see  plenty  in  dif- 
ferent parts  of  he  world,  were  made  first,  before  any  other 
rocks  were  laid  down  by  water.  Hutton  did  not  think  this  was 
true,  but  that,  on  the  contrary,  granite  might  be  even  now  form- 
ing deep  dowm  within  the  crust  of  the  earth.  But  how  was 
he  to  prove  this  ?  He  said  to  himself,  '  If  melted  granite 
forms  under  the  softer  strata  which  have  been  laid  down 
by  water,  it  ought  occasionally  to  obtrude  itself  into  them 
in  narrow  wedges  when  it  is  expanded  by  heat,  and  I  shall 
be  able  somewhere  to  find  veins  of  granite  piercing  the 
rocks  above.' 


222 


EIGHTEENTH  CENTURY. 


FT.   U\, 


To  prove  whether  this  was  so  he  made  a  journey  to  the 
Grampians,  where  there  are  large  masses  of  granite  ;  and 
there,  in  Glen  Tilt,  he  found  the  veins  of  red  granite  branch- 
ing out  into  the  clay-slate  and  limestone  rocks  above,  as 
in  Fig.  37.  It  is  easy  in  this  diagram  to  see  that  the 
water-made  layers,  «,  b,  must  have  been  there  before  the 
granite  was  melted,  otherwise  it  could  not  have  sent  the 
straggling  veins,  c  c,  up  into  them.  And  so  he  convinced 
himself  that  softie  granites  are  newer  than  the  aqueous  rocks 
which  lie  above  them.     It  is  said  that  he  was  so  delighted 

Fig.  37. 


Granite  Veins  in  Glen  Tilt. 
a.  Clay  slate,     b.  Limestone,     c.  Granite  veins. 

at  finding  this   proof  that  the  guides  who  were  with  him 
thought  he  had  discovered  a  vein  of  gold. 

This  is  one  out  of  many  examples  of  the  way  in  which 
Hutton  worked  and  corrected  the  mistakes  which  had 
sprung  up  in  the  German  school  of  geology.  Werner  had 
taught  his  pupils  that  there  was  really  something  to  be  learnt 
from  the  study  of  the  rocks ;  that  they  could  be  made  to 
tell  real  histories  of  the  past  and  help  men  to  get  wealth  for 
the  future,  and  thus  he  persuaded  them  to  give  time  and 
thought  to  this  work.  Hutton  showed  that  to  carry  on  this 
study  rightly  they  must  open  their  eyes  to  all  that  is  going 


CH.  XXVI.  WILLIAM  SMITH.  223 

on  now,  and  that  the  only  way  to  read  the  history  of  the 
past  is  to  compare  it  with  the  present. 

"William  Smith  surveys  the  Rocks  of  England. — Mean- 
while another  man,  whom  we  must  not  forget  to  mention,  was 
working  away  very  quietly  without  any  help,  and  with  very 
little  money  \  and  yet  in  his  way  was  doing  at  least  as  much 
work  as  the  others.  This  was  William  Smith,  a  plain  Eng- 
lish surveyor,  who  was  so  much  struck  with  the  arrange- 
ment of  the  different  formations  in  the  hills  among  which 
he  travelled  that  he  determined  to  try  and  map  them  out 
so  as  to  show  exactly  how  the  strata  are  placed  one  above 
the  other,  and  what  counties  they  pass  through. 

He  began  his  work  in  1 790,  and  travelled  over  the  whole 
country,  chiefly  on  foot,  marking  as  he  went  all  the  different 
positions  of  the  rocks,  and  collecting  the  shells  and  other 
fossils  which  he  found  in  them.  He  had  not  gone  on  long 
before  he  observed  that  certain  fossils  which  appeared  in  the 
lower  beds  disappeared  when  he  reached  those  which  lay 
above  them,  and  that  others  took  their  place ;  so  that  in  this 
way  it  was  possible  to  use  the  fossils  to  trace  out  the  age  of 
any  particular  rock,  just  as  the  face  of  a  coin  helps  you  to 
tell  the  reign  in  which  it  was  cast ;  and  the  story  told  by 
the  fossils  agreed  very  well  with  the  divisions  which  he  had 
worked  out  by  the  position  of  the  rocks  above  each  other. 
He  was  even  so  observant  that  he  distinguished  between 
the  fossils  which  had  their  edges  fresh,  showing  that  they 
had  not  been  disturbed  since  they  were  buried  in  the  earth, 
and  those  which  were  rubbed  and  water-worn.  The  fresh 
ones  only,  he  said,  are  of  use  to  tell  the  age  of  a  rock,  for 
those  which  are  rubbed  may  have  been  washed  out  of  some 
older  formation  by  rivers. 

In  this  way  William  Smith,  for  pure  love  of  science,  and 


224  EIGHTEENTH  CENTURY,  pt.  hi. 

without  any  hope  of  gain,  travelled  over  the  whole  of  Eng- 
land and  Wales,  mapping  out  the  rocks  and  noticing  all 
their  peculiarities.  In  1799  he  published  a  list  or  tabular 
view  of  the  formations  with  their  fossils,  and  the  places 
where  they  might  be  seen  in  the  hills;  and  in  18 15  he  at 
last  succeeded  in  completing  a  geological  map  of  England, 
which  has  ever  since  formed  the  foundation  of  our  British 
geology,  and  which  remains  a  lasting  monument  of  what  one 
man  may  accomplish  by  patience  and  indefatigable  industry. 
William  Smith  fairly  earned  the  title  of  the  '  Father  of  Eng- 
lish Geologists,'  which  has  ever  since  been  given  him,  and, 
with  Werner  and  Hutton,  deserves  to  be  remembered  as  one 
of  the  founders  of  the  science  of  geology. 


Chief  Works  consulted. — Lyell's  'Principles  of  Geology;'  Lyell's 
*  Student's  Elements  of  Geology  ; '  Page's  '  Advanced  Text-Book  of 
Geology  ; '  Hutton's  '  Theory  of  the  Earth  ;'  Fitton's  'Notes  on  Pro- 
gress of  Geology  in  England  ; '  '  Life  of  Werner '  —  '  Naturalists' 
Library,'  vol.  xxxix. 


CH.  XXVII.  MODERN  CHEMISTRY.  225 


CHAPTER  XXVn. 

SCIENCE   OF   THE   EIGHTEENTH   CENTURY   (CONTINUED). 

Birth  of  Modern  Chemistry — Discovery  of  'Fixed  Air,'  or  Carbonic 
Acid,  by  Black  and  Bergmann  —  Working  out  of  *  Chemical 
Affinity '  by  Bergmann  —  He  tests  Mineral   Waters,   and  proves 

*  Fixed  Air '  to  be  an  Acid — Discovery  of  Hydrogen  by  Cavendish 
- — He  Investigates  the  Composition  of  Water — Oxygen  discovered  by 
Priestley  and  Scheele — Priestley's  Experiments — He  fails  to  see  the 
true  bearing  of  his  Discovery — His  Political  Troubles  and  Death 
—  Nitrogen  described  by  Dr.  Rutherford  —  Lavoisier  lays  the 
Foundation   of  Modern   Chemistry — He  destroys   the   Theory   of 

*  Phlogiston '  by  proving  that  Combustion  and  Respiration  take  up  a 
Gas  out  of  the  Air — Discovers  the  Composition  of  Carbonic  Acid 
and  the  nature  of  the  Diamond — French  School  of  Chemistry — 
Death  of  Lavoisier. 

During  the  last  half  of  the  eighteenth  century,  while  Hunter 
and  Linn^us  were  adding  to  our  knowledge  of  living  beings, 
and  Werner  and  Hutton  were  reading  the  history  of  the 
crust  of  the  earth,  a  little  group  of  men  in  England,  France, 
and  Sweden  were  making  discoveries  which  entirely  altered 
the  science  of  chemistry.  These  men  were  Bergmann  and 
Scheele  in  Sweden ;  Black,  Cavendish,  and  Priestley  in  Eng- 
land ;  and  Lavoisier  in  France. 

In  order  to  understand  what  their  discoveries  were,  and 
what  they  taught  us,  it  is  necessary  to  bear  in  mind  that  up 
to  this  time  chemists  had  believed  fire,  air,  and  water  to  be 
simple  substances  which  could  not  be  decomposed  or  split 
up  into  any  other  kind  of  matter.      Mayow,  indeed,  had 


226  EIGHTEENTH  CENTURY.  pt.  hi. 

shown  that  the  atmosphere  could  be  separated  into  two 
gases,  but  his  experiments  had  been  passed  over  and  for- 
gotten; and  though  Dr.  Hales,  at  the  beginning  of  the 
eighteenth  century,  had  collected  several  gases,  he  had  not 
distinguished  them  from  air.  The  fact  was  that  Stahl's 
imaginary  '  phlogiston,'  which  was  supposed  to  pass  out  of 
burning  and  breathing  bodies  into  the  air,  was  a  constant 
source  of  confusion,  and  led  men  away  from  the  truth. 

But  the  time  had  now  come  when  these  misty  ideas  were 
to  be  dispelled,  by  the  discovery  of  the  four  gases — carbonic 
acid,  hydrogen,  oxygen,  and  nitrogen. 

Discovery  of  '  Fixed  Air,'  or  Carbonic  Acid,  by  Black, 
1756. — The  first  step  was  made  by  a  Scotch  physician 
named  Black,  who  was  bom  in  1728,  and  became  Professor 
of  Chemistry  at  Glasgow  in  1756.  Here  he  made  many 
valuable  experiments,  and  among  other  things  he  was  very 
anxious  to  find  out  why  limestone  altogether  changes  its 
character  when  it  is  burnt.  If  you  take  a  piece  of  ordinary 
limestone  or  chalk,  and  put  it  in  water,  it  will  remain 
without  any  change  unless  you  add  a  little  acid  to  the 
water,  and  then  the  limestone  will  effervesce,  and  bubbles 
will  begin  to  rise  up  from  it.  But  if  you  take  a  piece 
of  the  same  limestone  and  burn  it  in  a  fire,  it  turns  into 
a  powder  called  quick-lime,  v/hich  will  no  longer  give  out 
bubbles  when  you  pour  acid  upon  it,  but  directly  you  mix 
it  with  water  it  will  swell  up  and  become  intensely  hot, 
as  you  may  see  for  yourself  if  you  watch  bricklayers  making 
mortar  by  the  roadside.  This  complete  change  in  the  lime- 
stone, caused  by  merely  heating  it,  had  been  a  great  problem 
to  chemists;  and  Dr.  Black  was  still  more  puzzled  by  finding 
that  the  lime  was  lighter  after  it  had  been  burnt,  although 
he  could  not  discover  that  it  had  lost  anything  except  a  Httle 


CH.  XXVII. 


BLACK'S  'FIXED  AIR: 


22'/ 


water,   which   was  not  enough  to  account  for  the   loss  of 
weight. 

At  last  he  remembered  that  Dr.  Hales  had  driven  air  out 
of  substances,  and  collected  it  in  bottles ;  and  he  began  to 
consider  whether  the  heat  of  burning  might  not  have  driven 
some  heavy  kind  of  air  out  of  the  limestone,  and  so  made  it 
lighter.  To  prove  this  he  made  the  experiment  which  has 
since  been  always  used  for  making  small  quantities  of  car- 
bonic  acid  gas.  He  put  some  pieces  of  limestone  in  the 
bottle,  a.  Fig.  38,  and  poured  upon  them  some  water  and 

Fig.  -,8. 


Carbonic  Acid  rising  from  Limestone  and  Acidulated  Water  (Griffin). 

a.  Bottle  containing  pieces  of  limestone  in  water  and  acid,     b.   Connecting  tube. 

c.  Inverted  jar,  out  of  which  the  rising  gas  is  driving  the  water. 

some  acid.  He  then  stopped  the  bottle  with  a  tight  cork, 
and  joined  it  by  the  tube  ^  to  a  large  glass  jar,  c,  filled  with 
water,  and  standing  with  its  open  end  downwards  in  a 
vessel  of  water.  In  a  few  moments  the  bubbles  began  to 
rise  from  the  limestone,  and  passing  into  the  jar,  c,  drove 
out  the  water  and  filled  the  jar  with  gas. 

This  gas  Black  called  '  fixed  air,'  because  it  had  been 
fixed  in  the  limestone  before  it  was  driven  out  by  the 
acid.    He  collected  and  weighed  it,  and  found  that  it  exactly 


228  EIGHTEENTH  CENTURY.  pt.  hi. 

made  up  the  weight  which  the  limestone  had  lost.  He  then 
reversed  the  experiment,  and  taking  some  water  which  had 
lime  dissolved  in  it,  he  passed  some  'fixed  air'  into  it,  and, 
as  he  expected,  the  gas  joined  itself  to  the  lime  and  formed 
a  powdered  white  chalk  at  the  bottom  of  the  bottle.  By 
these  two  experiments  he  proved  that  limestone  is  composed 
of  lime  and  *  fixed  air.' 

He  then  proceeded  to  examine  the  gas  itself.  He  found 
that  animals  died  in  it,  and  that  a  flame  would  not  burn  in 
it,  and  also  that  it  was  the  same  gas  as  that  which  bubbles 
out  of  beer  and  other  liquids  when  they  ferment,  and  often 
out  of  mineral  springs.  He  also  proved  that  there  is  '  fixed 
air '  in  our  breath,  by  breathing  into  a  glass  of  lime-water, 
and  thus  forming  powdered  chalk,  which  fell  to  the  bottom 
of  the  glass. 

All  this  Black  discovered  about  '  carbonic  acid,'  which  is 
sometimes  called  '  fixed  air '  even  now,  when  people  speak 
of  it  in  efiervescing  drinks.  He  did  not  know  that  it  is  an 
acid ;  this  discovery  was  made  by  Bergmann  of  Sweden,  of 
whom  we  must  now  speak. 

Bergmann  shows  that  Fixed  Air  is  an  Acid — Works 
out  'Chemical  Affinity'  of  many  Substances. — Torbern 
Bergmann,  who  was  born  in  1735  in  West  Gothland,  was 
the  son  of  a  tax-collector,  and  he  had  the  greatest  difficulty 
in  getting  permission  to  study  science.  His  father  had  in- 
tended him  for  the  law  or  the  church,  and  it  was  not  until 
his  scientific  books  had  been  burnt,  and  he  had  fallen  ill 
with  disappointment,  that  they  saw  it  was  useless  to  oppose 
him,  and  he  was  allowed  to  take  his  own  course.  From 
that  time  he  was  happy ;  he  put  himself  under  the  great 
Linnseus,  and  in  1761  became  Professor  of  Natural  Philo- 
sophy at  Upsala,  and  afterwards  of  Chemistry  at  Stockholm. 


CH.  xxvii.  CHEMICAL  AFFINITY.  229 

Bergmann  made  a  great  advance  in  chemistry  by  working 
out  the  '  che7nical  affinity '  of  many  substances,  and  showing 
how  to  make  use  of  it  to  test  or  try  mineral  waters. 

Nearly  a  hundred  years  before  Bergmann  began  to  study 
chemistry,  Newton,  when  writing  on  attraction,  had  pointed 
out  that  when  substances  are  mixed  together  some  kinds 
attract  each  other  very  strongly  and  join  together,  making 
one  compound  substance.  For  instance,  he  said,  if  you 
put  copper  into  nitric  acid  the  copper  will  dissolve  and  dis- 
appear ;  but  if  you  plunge  a  piece  of  iron  into  the  liquid  the 
copper  will  re-appear  and  fall  to  the  bottom  of  the  glass, 
because  the  iron  attracts  the  nitric  acid  more  strongly  than 
the  copper  does,  and  so  it  takes  it  up  out  of  the  liquid, 
setting  the  copper  free. 

Chemists  had  till  now  neglected  this  observation  of 
Newton's,  but  Bergmann  followed  it  out,  and  by  a  number 
of  experiments  he  made  out  a  table  of  those  substances 
which  seemed  to  have  the  greatest  affinity  for  each  other, 
and  which  would  unite  whenever  the  conditions  would  allow 
them.     This  he  called  a  table  of  '  elective  affinities.^ 

It  is  easy  to  see  how  this  could  be  used  for  testing  or 
trying  what  substances  lie  hidden  in  mineral  waters.  Iron, 
for  instance,  in  the  case  given  by  Newton,  would  show  when 
copper  was  dissolved  in  a  liquid  containing  nitric  acid. 
Boyle,  too,  had  shown  that  a  blue  liquid  extracted  from  the 
lichen  called  lit^nus  turns  to  a  bright  red  directly  it  touches 
an  acid  j  so  that  blue  litmus  is  a  sure  test  of  an  acid.  Again, 
common  salt  put  into  a  clear  liquid  containing  silver,  turns 
it  cloudy ;  while  tincture  of  gall-nuts  makes  a  purple  cloud 
in  a  solution  containing  iron.  Bergmann  worked  out  a 
number  of  these  tests^  and  by  means  of  them  analysed  or 
separated  out  the  substances  contained  in  mineral  waters ; 


230  EIGHTEENTH  CENTURY.  PT.  ni. 

he  even  melted  solid  minerals  in  acids  and  tested  them  in 
the  same  way. 

One  of  the  first  uses  that  he  made  oif  his  tests  was  to  try- 
Black's  'fixed  air.'  When  he  heard  of  this  gas  he  suspected 
that  it  must  be  an  acid,  because  it  Joined  itself  to  lime, 
which  is  an  alkali,  that  is,  a  substance  in  all  respects  unlike 
an  acid ;  and  he  had  found  that  unlike  substances  nearly 
always  attract  each  other  most  strongly.  So  he  made 
some  '  fixed  air '  and  tested  it  with  blue  litmus,  and,  as  the 
litmus  turned  red  directly,  he  knew  that  he  was  right  in 
supposing  it  to  be  an  acid,  and  he  called  it '  aerial  acid,'  or 
acid  air.  He  then  weighed  it  and  proved  that  it  was  heavier 
than  common  air,  and  bypassing  it  through  water  he  showed 
that  a  large  quantity  of  it  would  dissolve. 

Thus  these  two  men,  Black  and  Bergmann,  had  arrived 
at  a  pretty  good  knowledge  of  this  gas.  They  had  proved 
that  it  is  an  invisible  heavy  kind  of  air ;  that  it  dissolves  in 
water  ;  that  it  is  acid  and  joins  itself  to  lime,  forming  Hme- 
stone  or  chalk ;  that  it  destroys  life  when  breathed,  and 
puts  out  a  flame ;  that  it  is  given  out  by  fermenting  liquids, 
and  from  mineral  springs,  and  is  contained  in  our  breath. 
One  thing  they  had  not  found  out,  namely,  that  it  is  made 
up  of  two  elements  ;  this,  as  you  will  see  (p.  238),  was  dis- 
covered by  Lavoisier  in  1779,  when  he  gave  it  the  name  of 
*  carbonic  acid.' 

Discovery  of  Hydrogen  by  Cavendish,  1766. — The  next 
gas  discovered  was  hydrogen,  and  its  discoverer  was  Henry 
Cavendish,  grandson  of  the  Duke  of  Devonshire,  who  was 
bom  in  1731.  Cavendish  was  a  very  shy  and  reserved  man, 
who  lived  much  alone  and  found  his  greatest  pleasure  in 
studying  science  for  its  own  sake.  It  is  even  related  of  him 
that  he  taught  all  his  servants  to  understand  by  signs  what 


CH.  XXVII.  HYDROGEN  AND   OXYGEN.  231 

he  wanted  in  order  that  he  might  be  able  to  think  without 
interruption. 

In  the  year   1766   he  read  a  paper  before   the  Royal 

Society  upon   a  gas   which   he   called    '  inflammable   air/ 

because  it  burst  into  a  flame  whenever  a  light  was  brought 

near  it,  and  also  because  he  believed  it  to  be  the  cause  of 

the  explosions  which  so  often  take  place  in  mines.     He 

obtained  this  gas  by  pouring  sulphuric  acid  and  water  upon 

zinc,  iron,  or  tin,  and  then  collecting  the  bubbles  as  Black 

had  done  (see  Fig.  38,  p.  227).    But  when  he  began  to  make 

experiments  with  this  gas  he  found  it  very  different  from 

Black's  '  fixed  air.'     It  is  true  that  a  candle  would  not  burn, 

nor  could  animals  breathe  in  it ;  but  when  a  light  was  brought 

near  it,  it  took  fire  and  burnt  with  a  pale  blue  flame  inside 

the  bottle.  Then  instead  of  being  heavy  like  '  fixed  air,'  it  was 

lighter  than  the  atmosphere,  and  for  this  reason  it  was  soon 

used  for  filling  balloons.     It  had  also  another  remarkable 

peculiarity,  that  when  mixed  with  air  in  a  bottle,  it  exploded 

with  a  loud  noise  directly  a  light  was  brought  near  it,  leaving 

drops  of  moisture  inside  the  bottle.     Cavendish  did  not 

understand  the  cause  of  this  explosion  at  first,  but  in^  1784 

(after  Priestley  had  discovered  oxygen)  he  mixed  pure  oxygen 

and  hydrogen  in  a  closed  vessel,  and  lighted  them  by  an 

electric  spark,  and  then  he  made  the  great  discovery  that 

these  two  gases,  when  lighted,  rush  together  and  form  zvater, 

which  is  therefore  a  compound  substance  made  of  oxygen 

and  hydrogen. 

Oxygen  discovered  by  Priestley  in  1774,  and  by  Scheele 
in  1775. — The  next  gas  discovered  was  oxygen,  the  most 
common  and  the  most  useful  of  all  the  substances  in  our 
globe.  It  was  discovered  independently  by  two  men — 
Priestley,  a  dissenting  minister  at  Leeds,  and  Scheele  (born 


232  EIGHTEENTH  CENTURY.  pt.  hi. 

1742),   a  small  apothecary   at  Kj5ping,    a  little  village  in 
Sweden. 

There  is  no  doubt  that  Scheele  deserves  as  much  credit 
for  this  discovery  as  if  Priestley  had  never  made  it,  for  he  had 
not  heard  of  his  experiments,  and  he  added  many  useful 
facts  which  Priestley  did  not  know.  Still,  as  they  both  went 
over  much  the  same  ground,  we  cannot  afford  space  here  to 
give  Scheele's  experiments.  You  must  not,  however,  forget 
his  claim,  for  though  the  world  often  forgot  him  because  he 
remained  a  poor  apothecary  all  his  life,  yet  Scheele  was 
really  one  of  the  first  chemists  of  Europe.  We  owe  to  him 
the  discovery  of  chlorine ;  and  of  manganese,  barytes,  fluor- 
spar, and  many  other  earths  whose  names  I  cannot  expect 
you  to  know.  Indeed,  his  merit  was  so  great  that  Bergmann, 
his  friend  and  patron,  once  said,  '  The  greatest  discovery  he 
ever  made  was  when  he  discovered  Scheele.' 

Joseph  Priestley,  the  discoverer  of  oxygen,  was  born  in 
1733-  The  greater  part  of  his  life  was  spent  in  writing  upon 
religious  subjects,  and  it  was  only  in  his  leisure  hours  that 
he  studied  chemistry.  He  tells  us  in  his  autobiography  that 
he  first  began  to  take  an  interest  in  such  things  in  conse- 
quence of  visiting  a  brewery  next  door  to  his  house  and 
watching  the  fixed  air  which  rose  from  the  beer-vats.  His 
first  chemical  experiment  of  any  value  was  to  force  this  '  fixed 
air '  into  pure  water^  thus  making  an  effervescing  drink  much 
the  same  as  the  soda-water  we  drink  now.  He  next  tried 
what  effect  growing  plants  have  upon  air,  and  by  keeping  a 
pot  of  mint  under  a  bell-jar  in  which  the  air  had  been  spoilt 
by  burning  or  breathing,  he  proved  that  plants  take  up  the 
bad  air  and  render  the  remainder  fit  again  to  support  a 
flame  or  life.  He  did  not,  however,  yet  know  why  this  took 
place.     He  also  invented  a  number  of  troughs  and  other 


CH.  XXVII. 


PRIESTLEY'S  DISCOVERIES. 


233 


apparatus  for  collecting  and  washing  gases,  and  amused 
himself  as  Hales  had  done  in  driving  gas  out  of  different 
substances. 

And  thus  it  happened  that  one  day,  August  1,  1774,  he 
made  an  experiment  which  led  to  a  great  discovery.  He 
took  a  red  powder  called  mercuric  oxide^  which  he  knew 
contained  mercury  and  something  else  besides,  and  he  put 
it  into  the  bulb,  a^  Fig.  39  ;  the  rest  of  the  tube  he  filled 

Fig.  39. 


Priestley's  Apparatus  for  procuring  Oxygen. 

a.  Bulb  containing  red  mercuric  oxide,    h,  Vessel  containing  mercury,     c.  Inverted 
jar  for  collecting  the  gas.     d,  Burning  glass. 

with  mercury,  and  passed  it  into  the  basin  b,  and  up 
into  the  jar  r,  both  h  and  c  being  also  filled  with  mercury. 
He  next  took  a  powerful  burning-glass,  d^  and  brought  the 
rays  of  the  sun  to  a  focus  upon  the  red  powder.  As  soon 
as  the  powder  became  very  hot  a  gas  rose  out  of  it  and 
passed  along  the  tube  into  the  jar,  <:,  driving  out  the  mer- 
cury j  while  the  red  colour  began  to  disappear  in  the  bulb, 
a,  and  only  pure  shining  mercury  remained  behind.  So  far 
he  ?iad  only  proved  that  red  mercuric  oxide  is  made  up  of 
mercury  and  a  gas. 

When  he  had  collected  enough  gas  to  experiment  upon, 


234  EIGHTEENTH  CENTURY.  pt.  hi. 

he  passed  some  of  it  through  water  and  found  that  it  did  not 
dissolve  as  '  fixed  air '  does  j  but  what  surprised  him  still 
more  was  that  a  candle  put  into  it  burnt  with  a  large 
vigorous  flame,  and  a  piece  of  red-hot  charcoal  burst  into 
flame  in  it  and  burnt  furiously.  It  was  clear  then  that  this 
could  not  be  either  '  fixed  air '  or  '  inflammable  air/  for 
neither  of  these  would  feed  a  flame.  He  next  put  two  mice 
into  some  of  the  gas,  and  he  found  that  they  lived  much 
longer  than  in  ordinary  air.  When  he  breathed  it  also  into 
his  own  chest  he  felt  singularly  light  and  easy  for  some  time 
afterwards.  *  Who  can  tell,'  he  writes,  *  whether  this  pure 
air  may  not  at  last  become  a  fashionable  luxury?  As  yet 
only  two' mice  and  myself  have  had  the  privilege  of  breathing 
it.' 

Here,  you  see,  we  have  come  back  again  to  Mayow's 
fire-air,  so  long  forgotten,  which  supports  life  and  flame. 
Priestley  had  learnt  more  about  it  than  Mayow  had,  for  he 
had  collected  it  separately,  had  burnt  it,  and  breathed  it  with- 
out other  air  being  mixed  with  it ;  and  he  had  moreover 
shown  that  it  could  be  driven  out  of  metallic  compounds, 
for  mercury  is  a  metal.  Yet  it  is  disappointing  to  learn  that, 
in  spite  of  having  gone  thus  far,  Priestley  was  so  imbued 
with'Stahl's  theory  of  'phlogiston,'  that  he  did  not  really 
understand  the  great  discovery  he  had  made,  but  called  his 
gas  *  dephlogisticated  air,'  or  air  which  had  lost  that 
imaginary  '  phlogiston '  which  was  always  confusing  men's 
minds. 

There  is  no  doubt  that  he  discovered  the  gas  and  showed 
that  it  was  the  chief  actor  in  combustion  and  respiration, 
and  for  this  discovery  and  that  of  an  immense  number  of 
other  gases,  he  was  elected  a  member  both  of  the  Royal 
Society  and  the  Academic  des  Sciences,  and  his  fame  was 


CH.  XXVII.  NITROGEN.  235 

great  all  over  Europe  ;  yet  still  he  had  not  hit  upon  the 
entire  truth — he  had  given  the  facts,  and  it  remained  for 
Lavoisier  to  read  the  riddle. 

Besides  his  chemical  writings,  Priestley  published  many 
books  on  theology,  and  though  he  was  a  singularly  gentle 
quiet  man,  yet  his  religious  and  political  essays  were  often 
very  severe,  and  they  led  to  his  being  driven  out  of  Bir- 
mingham, and  his  house  burnt  by  the  mob,  when  they  at- 
tacked the  leading  Dissenters  during  the  panic  caused  by 
the  French  Revolution.  After  living  for  some  time  near 
London  he  emigrated  to  America,  where  he  died  in  1804. 
He  continued  his  chemical  experiments  up  to  the  time  of 
his  death,  and  made  many  important  discoveries,  but  the 
chief  discovery  which  will  always  be  connected  with  his 
name  was  that  oi  oxygen,  in  1774. 

Properties  of  Nitrogen  determined  by  Dr.  Rutherford 
in  1772. — There  now  remains  to  be  mentioned  only  one  of 
the  four  gases  spoken  of  at  page  226,  namely,  nitrogen. 
This  gas  was  first  properly  described  by  Dr.  Rutherford  in 
1772,  but  there  is  very  little  to  be  said  of  it  except  that  it 
has  scarcely  any  of  those  properties  which  belong  to  the 
other  gases.  It  does  not  support  life  or  flame  like  oxygen ; 
it  does  not  make  lime-water  cloudy  as  carbonic  acid  does, 
nor  does  it  burn  like  hydrogen.  In  fact,  it  is  a  dull  sleepy 
gas,  which  remains  after  oxygen  has  been  taken  out  of  the 
air,  and  which  can  be  driven  out  of  many  solid  bodies, 
especially  nitre  or  saltpetre. 

Lavoisier  lays  the  Foundation  of  Modern  Chemistry, 
1778. — The  determination  of  nitrogen  completes  the  history 
of  the  discovery  of  those  gases  of  which  fire,  air,  and  water 
are  composed  ;  but  you  will  have  noticed  that  we  have  not 
yet  arrived  at  the  new  explanation  of  chemical  changes  which 


236  EIGHTEENTH  CENTURY.  pt.  iir. 

was  to  take  the  place  of  *  phlogiston.'  The  fact  is  that 
Black,  Bergmann,  Cavendish,  Scheele,  and  Priestley,  were  all 
so  cramped  by  the  old  theory,  that  though  they  discovered 
the  facts  they  could  not  make  the  right  use  of  them.  The 
man  who  did  this,  and  who  laid  the  foundation  of  modern 
chemistry,  was  the  celebrated  French  chemist,  Lavoisier. 

Antoine  Laurent  Lavoisier  was  bom  in  Paris  in  1743. 
His  father,  who  was  a  wealthy  merchant,  gave  him  a 
splendid  education,  and  when  he  was  still  quite  young  the 
new  discoveries  which  were  being  made  in  chemistry  tempted 
him  to  learn  that  science.  At  twenty-one  years  of  age  he 
received  a  gold  medal  from  the  Academie  des  Sciences  for 
a  very  elaborate  and  learned  essay  on  the  best  way  of  light- 
ing the  streets  of  Paris.  At  five-and-twenty  he  was  elected 
a  member  of  the  Academie,  and  from  that  time  he  deter- 
mined to  devote  his  life  to  chemistry. 

As  early  as  1770  Lavoisier  had  begun  to  suspect  that 
the  famous  theory  of  phlogiston  was  false.  His  chief  reason 
for  thinking  this  was  that  he  found,  as  Geber  had  done  more 
than  900  years  before  (see  p.  44),  that  when  metals  are 
heated  so  that  they  turn  into  powder,  the  powder  weighs 
more  than  the  original  metal  did  before  it  was  heated. 
Moreover,  he  also  found  that  the  air  which  remained  behind 
in  the  vessel  in  which  the  metal  had  been  heated  had  lost 
exactly  as  much  weight  as  the  metal  had  gained.  So  it  seemed 
to  him  clear  that  the  metal  must  have  taken  something y9'^w. 
the  air  instead  of  giving  anything  to  it. 

For  eight  years  Lavoisier  worked  incessantly  at  this 
problem.  He  heated  many  metals,  such  as  iron,  lead,  tin, 
&c.,  and  other  substances  such  as  sulphur  and  phosphorus, 
and  in  every  case,  if  he  collected  all  that  remained,  he  found 
it  heavier  than  before.    But  there  was  one  point  in  which  he 


CH.  XXVII. 


LA  VOISIER'S  EXPERIMENTS. 


237 


could  not  succeed  j  he  could  not  make  the  metals  give  back 
again  what  they  had  taken  from  the  air,  so  that  he  might 
examine  it.  At  last,  in  1778,  it  occurred  to  him  that 
Priestley  had  separated  mercuric  oxide  into  two  substances  ; 
namely,  the  metal  mercury  and  a  gas.  Here,  then,  was  just 
the  step  he  wanted.  If  he  could  first  make  mercuric  oxide 
by  heating  mercury  in  the  air,  and  then  afterwards  separate 
it  back  again  into  mercury  and  a  gas,  he  would  thus  prove 
what  it  had  taken  out  of  the  air.  He  therefore  took  some 
mercury  and  put  it  into  a  tube  a,  Fig.  40,  which  was  connected 

Fig.  40. 


Lavoisier's  Apparatus  for  Heating  Mercury  and  making  it  take  up  Oxygen. 

A,  Bulb  containing  mercury.     B,  Vessel  containing  mercury,     c.  Bell-jar  partly  full 

of  air.     D,  Stove. 


with  a  bell- jar  c,  containing  air  and  standing  over  mercury. 
Then  he  heated  the  bulb  a  over  the  stove  d,  and  kept  the 
mercury  boiling  for  twelve  days. 

During  the  first  five  days  little  by  little  red  specks  began 
to  appear  on  the  top  of  the  mercury  in  c,  that  is,  mercuric 
oxide  was  formed ;  but  after  that  time,  when  about  one-fifth 
of  the  air  in  the  bell-jar,  c,  had  disappeared  and  mercury 
risen  in  its  place,  no  further  change  took  place.  He  then 
lifted  off  the  bell-jar  and  took  45  grains  of  this  red  powder 
and   made    Priestley's   experiment    with   it   (see    p.    233), 


238  EIGHTEENTH  CENTURY.  pt.  hi. 

and  he  obtained,  of  course,  the  gas  which  Priestley  had 
called  *  dephlogisticated  air.'  He  afterwards  found  by  more 
exact  experiments  that  the  amount  of  this  gas  contained  in 
the  mercuric  oxide  exactly  equalled  the  amount  lost  by  the 
air  in  which  the  mercury  had  been  heated. 

Now  see  what  Lavoisier  had  done  :  he  had  proved  that 
the  reason  why  air  shrinks  when  substances  are  burnt  in  it, 
is  because  the  substances  take  up  a  gas  out  of  the  air,  and  he 
had  also  shown  that  this  gas  is  the  same  as  that  which 
Priestley  discovered.  Now,  at  last,  the  false  theory  was 
destroyed,  and  the  starting-point  of  a  true  theory  was  found. 
The  imaginary  phlogiston,  which  had  been  supposed  to  load 
the  air  when  anything  was  burnt  in  it,  was  proved  never  to 
have  had  any  existence;  for  it  was  clear  that  just  the 
opposite  effect  takes  place.  All  burning  and  breathing  afid 
the  change  in  metals  is  caused  by  a  gas  being  taken  up  out 
of  the  air  and  joined  to  other  substances.  Lavoisier  called 
this  gas  oxygen  (from  o^vc,  acid  ;  ytwaM,  I  produce),  because 
he  found  that  most  substances  were  acid  after  they  had 
been  united  with  it.  This,  too,  led  him  to  suspect  that  as 
'  fixed  air '  was  an  acid,  and  could  be  made  by  burning  char- 
coal, it  must  be  composed  of  oxygen  and  carbon.  So  he 
burnt  small  quantities  of  charcoal  in  pure  oxygen,  and  by 
analysing  the  'fixed  air'  produced  proved  that  100  parts  by 
weight  of  this  gas  contained  72  parts  of  oxygen  and  28  of 
carbon.  For  this  reason  he  called  it  'carbonic  acid,'  a 
name  which  it  still  bears.  By  burning  a  diamond  in  oxygen 
and  producing  carbonic  acid,  he  also  proved  that  a  diamond 
is  pure  carbon. 

Lavoisier  had  very  great  difficulty  in  persuading  the 
other  leading  chemists  that  they  had  been  labouring  under  a 
false  idea,  and  that  substances  when  burning  do  not  put 


CH.  XXVII.     RAPID  ADVANCE    OF  CHEMISTRY.  239 

something  into  the  atmosphere  but  take  a  gas  out  of  it.  Dr. 
Black  was  one  of  the  first  to  be  convinced,  but  Priestley 
died  without  giving  up  his  old  opinions.  The  younger 
chemists,  however,  saw  the  truth  of  Lavoisier's  explanation, 
and  from  this  time  chemistry  advanced  very  rapidly. 
Lavoisier  invented  an  entirely  new  set  of  terms  instead  of 
the  old  names  of  the  alchemists,  and  though  his  terms  have 
been  greatly  altered  by  later  discoveries,  still  many  of  them 
will  always  be  used.  He  repeated  with  a  better  apparatus 
Cavendish's  experiment  of  turning  hydrogen  and  oxygen 
into  water,  and  he  gave  hyd^vgen  its  name  from  vlwp^  water, 
and  yEvvao),  I  produce.  Lastly,  he  published  his  *  Elements 
of  Chemistry,'  in  which  he  gave  a  clear  explanation  of  the 
different  chemical  changes,  and  how  students  could  work 
them  out  for  themselves. 

Lavoisier  was  now  at  the  height  of  his  fame,  full  of  his 
new  theory,  and  prepared  to  devote  the  rest  of  his  life  to 
making  chemistry  a  grand  science ;  but  a  very  sad  fate  was 
awaiting  him.  In  1793  the  great  French  Revolution  broke 
out  in  Paris.  Lavoisier  was  a  farmer-general,  that  is  a  kind 
of  collector  of  taxes,  and  all  the  farmers-general  were  hated 
by  the  people ;  so  he  knew  that  he  should  most  likely  lose 
all  his  fortune,  and  was  prepared  to  work  for  his  living ;  but 
he  had  not  expected  the  blow  which  fell  upon  him.  All  the 
farmers-general  were  condemned  to  death,  and  though  a 
physician  named  Halle,  who  deserves  always  to  be  remem- 
bered for  this  act,  pleaded  that  Lavoisier's  life  should  be 
spared  till  he  had  completed  his  experiments,  the  ignorant 
and  brutal  Government  replied,  '  We  do  not  need  learned 
men,'  and  on  May  18,  1794,  at  the  age  of  fifty-one,  Lavoisier 
was  guillotined. 

After  his  death  the  French  School  of  Chemistry  took  the 


240  EIGHTEENTH  CENTURY.  pt.  hi. 

lead  for  many  years,  until  new  discoveries  in  England,  which 
we  shall  mention  by-and-by,  made  another  great  advance. 
When  you  are  able  to  read  larger  works  upon  the  history  of 
chemistry  you  will  find  how  very  interesting  the  period  was 
of  which  we  have  been  speaking.  I  have  only  been  able  to 
give  you  here  the  very  barest  outline  of  it,  so  that  the  names 
of  these  great  chemists  may  not  be  quite  unfamiliar  when 
you  meet  with  them  in  other  books. 


Chief  Works  consulted. — 'Three  Papers  on  Factitious  Air,'  by 
Cavendish — 'Phil.  Trans.,'  1766;  Brande's  'Chemistry;'  Hoefer's 
*  Histoire  de  la  Chimie  ; '  Cuvier,  '  Histoire  des  Sciences  Naturelles  ; ' 
Huxley,  'On  Priestley' — 'Macmillan's  Magazine,'  1874;  Priestley,  *0n 
Different  Kinds  of  Air,'  1774  ;  Thomson's  '  Hist,  of  Royal  Society  ; ' 
Scheele's  '  Chemical  Experiments  on  Air  and  Fire,'  translated  1 780  ; 
Miller's  '  Elements  of  Chemistry ; '  Lavoisier's  '  Elements  of  Chemis- 
tr}','  translated  by  Kerr,  1790. 


CH.  xxviii.  DR.  BLACK.  24.1 


CHAPTER  XXVIII. 

SCIENCE   OF   THE    EIGHTEENTH    CENTURY  (CONTINUED). 

Doctrine  of  Latent  Heat,  taught  by  Dr.  Black  in  1 760 — Water  con- 
taining Ice  remains  always  at  0°  C,  and  Boiling  Water  at  100°  C, 
however  much  Heat  is  added — Black  showed  that  the  lost  Heat  is 
absorbed  in  altering  the  condition  of  the  Water — Watt's  Applica- 
tion of  the  Theory  of  Latent  Heat  to  the  Steam-engine — Early  His- 
tory of  Steam-engines — Newcomen's  Engine — Watt  invents  the 
Separate  Condenser — Diagram  of  Watt's  Engine — Difficulties  of 
Watt  and  Boulton  in  introducing  Steam-engines. 

Discovery  of  Latent  Heat  by  Dr.  Black  in  1760. — ^We 

must  now  go  back  a  few  years,  to  the  time  when  Dr.  Black 
was  lecturing  at  Glasgow  in  1760;  for  he  then  made  a 
remarkable  discovery  about  heat,  which  belongs  to  the 
history  of  physics  rather  than  of  chemistry.  This  was 
the  discovery  of  latent  heat,  or  of  heat  which  becomes  lost 
or  hidden  whenever  ice  is  turned  into  water,  or  water  into 
steam. 

If  you  put  a  lump  of  ice  in  a  saucepan  on  a  stove,  and 
when  it  begins  to  melt  stir  it  gently  so  as  to  keep  the  water 
well  mixed,  you  will  find  that  so  long  as  the  smallest  piece  of 
ice  is  left  in  the  water,  a  thermometer  standing  in  the  sauce- 
pan will  not  rise  higher  than  0°  Centigrade,  or  the  melting- 
point  of  ice.  Now  the  heat  from  the  stove  must  be  con- 
tinually entering  the  water,  otherwise  the  ice  would  not  melt. 
What  then  becomes  of  this  heat  ?•  Again,  if  you  keep  the 
water  on  the  stove  after  the  ice  is  melted,  it  will  grow  hotter 
12 


242       '  EIGHTEENTH  CENTURY.  PT.  III. 

and  hotter  till  it  reaches  ioo°  Centigrade,  when  it  will  boil. 
Here,  again,  it  will  remain  at  the  same  temperature,  and 
though  you  go  on  boiling  it  till  it  has  all  passed  away  in  steam, 
the  last  drop  of  water  will  never  be  hotter  than  ioo°  C.  So 
that  here  again  the  heat  which  is  added  remains  hidden 
and  does  not  become  apparent.  This  last  fact  about  boiHng 
water  had  been  long  known  to  philosophers,  but  no  one  found 
any  explanation  of  it  until  Black  began  his  experiments  on 
melting  ice  j  and  he  then  came  to  the  conclusion  that  the 
heat  is  employed  in  altering  the  condition  of  the  water, 
hat  is,  in  changing  it,  in  the  one  case  from  solid  ice  into 
water,  and  in  the  other  from  water  into  a  vapour. 

He  proved  this  by  some  simple  experiments  which  are 
not  difficult  to  make.  He  took  two  glass  flasks,  and  filled 
one  with  ice  just  on  the  point  of  melting,  and  the  other  with 
an  equal  weight  of  ice-cold  water.  These  he  hung  in  a 
moderately  warm  room,  which  he  kept  all  the  time  at  the 
same  heat  (8° -5  C).  At  the  end  of  half  an  hour  the  ice- 
cold  water  had  risen  four  degrees  (from  0°  to  4°),  but  the 
melting  ice  remained  at  0°,  and  it  was  ten  hours  and  a  half 
before  the  ice  had  disappeared  and  the  water  had  reached 
the  same  temperature  as  that  which  tlie  water  in  the  other 
basin  had  attained  in  half  an  hour.  Now  the  melting  ice 
had  been  receiving  heat  for  twenty-one  half-hours,  and 
therefore  had  taken  in  2 1  x  4,  or  84°  of  heat,  while  it  only 
showed  a  rise  of  4°.  It  was  clear,  therefore,  that  the  re- 
maining 80°  must  have  been  spent  in  turning  the  ice  into 
water. 

Black  now  tried  the  same  thing  in  another  way.  He 
found  that  a  pound  of  water  at  79°  C.  would,  exactly  melt  a 
pound  of  ice.  So  he  again  took  two  vessels,  in  one  of  which 
he  put  a  pound  of  ice-cold  water  at  0°  and  a  pound  of  hot 


CH.  XXVIII.  LATENT  HEAT,  243 

water  at  79°,  and  when  they  were  properly  mixed  he  found, 
as  he  expected,  that  the  heat  of  the  mixture  was  half-way 
between  the  two,  that  is  39^°.  In  the  other  vessel  he  put  a 
pound  of  ice  at  0°  and  a  pound  of  hot  water  at  79°,  and 
here,  when  the  ice  had  disappeared,  the  mixture  still  re- 
mained at  0°,  showing  that  the  whole  79°  of  heat  in  the 
boiling  water  had  been  absorbed  in  melting  the  ice,  and 
remained  hidden  or  latent  in  the  two  pounds  of  water.  The 
latent  heat  of  water  is  therefore  between  79°  and  80°. 

We  know  now  what  becomes  of  this  heat,  as  you  will  see 
(chapter  xxxiv.)  in  the  history  of  the  science  of  the  nine- 
teenth century ;  but  the  first  step  was  to  prove  its  disappear- 
ance into  the  water,  and  this  we  ow^e  to  Black ;  as  well  as  the 
fact  that  still  more  heat  is  lost  in  turning  water  into  steam. 

This  last  fact  he  proved  by  filling  a  glass  bottle  half  full 
of  water,  corking  it  very  tightly,  and  then  heating  the  bottle 
till  the  water  began  to  boil.  He  was  obliged  to  do  this  very 
gently,  because  steam  expands  with  great  power,  and  he  did 
not  wish  to  drive  out  the  cork  or  break  his  bottle.  After  a 
little  time  the  water  ceased  boiling,  because  the  other  half 
of  the  bottle  was  full  of  steam,  and  there  was  no  room  for 
more  to  form.  But  now  the  water  began  to  grow  hotter 
and  hotter,  and  rose  above  100°  C,  showing  that  when  the 
heat  could  no  longer  form  steam  it  did  not  remain  hidden, 
but  increased  the  temperature  of  the  water.  At  last,  when 
he  was  afraid  to  heat  the  bottle  any  more,  he  loosened  the 
cork,  which  flew  out  with  great  violence,  followed  by  a  cloud 
of  steam.  And  now  notice  what  happened ;  directly  the 
rush  of  steam  was  over,  the  heat  of  the  water  in  the  bottle 
fell  again  to  100°  C,  for-  all  the  rest  of  the  heat  had  been 
used  in  foi'ming  more  steam  the  moment  the  pressure  was 
removed. 


244  EIGHTEENTH  CENTURY.  rx.  in. 

James  "Watt,  1736-1819. — Black  had  now  completed 
his  discovery,  and  from  that  time  he  taught  in  all  his 
lectures  that  heat  becomes  latent  or  absorbed  when  a  solid 
is  changed  into  a  liquid,  or  a  liquid  into  vapour.  It  was 
about  this  time  that  the  famous  engineer,  James  Watt,  began 
to  study  the  power  of  steam,  and  as  Black  was  his  friend, 
he  came  to  him  to  help  him  solve  his  difficulties.  The  his- 
tory of  the  steam-engine,  being  the  history  of  an  invention, 
does  not  strictly  belong  to  our  work ;  but  the  use  which 
Watt  made  of  the  discoveries  about  steam  is  a  part  of 
science,  and  we  must  therefore  find  room  for  a  slight  sketch 
of  it  here. 

James  Watt  was  born  at  Greenock  in  1736 ;  he  was  the 
son  of  a  builder  and  shipwright,  and  was  so  delicate  as  a 
child  that  he  was  kept  at  home,  and  learnt  reading  from  his 
mother,  and  writing  and  arithmetic  from  his  father.  When 
at  last  he  was  sent  to  school  he  found  it  hard  work,  for  he 
was  slow  and  thoughtful,  and  the  other  children  jeered  at 
him  for  his  want  of  quickness.  Everyone  knows  the  story 
of  his  being  scolded  by  his  aunt  for  sitting  silent  a  whole 
hour,  holding  first  a  spoon  and  then  a  saucer  over  the  steam 
rising  from  a  kettle,  and  watching  drops  of  water  gathering 
upon  them.  It  was  in  this  quiet  way  that  little  James's 
mind  grew,  and  it  may  be  an  encouragement  to  slow,  plod- 
ding boys  to  know  that  one  of  our  greatest  inventors  was 
considered  a  dull  and  backward  child. 

As  he  grew  older  James  went  up  to  London,  and  there, 
after  overcoming  many  obstacles,  which  the  guilds,  or  trades' 
unions  of  those  days,  put  in  the  way  of  all  independent 
workers,  he  learnt  to  make  mathematical  instruments,  and 
then  returned  to  Glasgow,  where  he  began  business.  Though 
he  was  only  one-and-twenty  he  soon  became  known  as  .a 


cii.  XXVIII.  JAMES   WATT.  245 

man  of  unusual  ability,  for  the  mind  of  the  dull  boy  had 
developed,  and  his  thoughtfulness  had  begun  to  produce 
results.  Not  only  the  students,  but  even  the  professors  of 
the  University  used  to  stroll  into  his  little  shop  to  discuss  the 
discoveries  of  the  day.  '  Whenever  any  difficulty  arrested 
us,'  writes  a  student  named  Robison,  '  we  used  to  run  to  our 
workman,  and  he  never  let  go  his  hold  until  he  had  entirely 
cleared  up  the  proposed  question.'  One  day  it  was  neces- 
sary to  read  a  German  book  on  mechanics ;  Watt  imme- 
diately set  to  work  and  learnt  German,  and  another  time, 
for  the  same  reason,  he  studied  the  Italian  language.  It  is 
scarcely  surprising  that  a  man  with  such  talent  and  perse- 
verance as  this,  who  was  also  gentle  and  loving  to  every- 
body, should  be  sought  after  both  by  masters  and  students. 

Among  those  who  came  to  Watt's  shop  was  one  Ander- 
son, professor  of  physics,  who,  finding  that  a  little  model  of 
a  steam-engine  in  the  University  museum  was  out  of  order, 
brought  it  to  Watt  to  be  repaired,  and  thus  led  the  way  to 
his  invention.  And  here  it  is  necessary  to  point  out  two 
things  :  First,  you  must  not  suppose  that  by  a  steam-engine 
is  meant  a  railway  engine  ;  all  contrivances  which  move  by 
the  power  of  steam  are  steam-engines,  and  locomotive  engines 
which  draw  carriages  were  not  made  till  1804,  long  after  Watt's 
time.  Secondly,  you  must  get  rid  of  the  idea,  which  many 
people  have,  that  Watt  was  the  first  man  to  make  an  engine 
which  moved  by  steam.  This  was  done  long  before  his  time. 
The  thing  which  Watt  really  did  was  to  make  an  engine  such 
as  we  now  use,  working  entirely  by  steam,  without  the  help 
of  air,  and  doing  an  enormously  greater  amount  of  work  with 
the  same  quantity  of  fuel  than  any  others  had  done  before. 

The  Newcomen  Engine,  1705. — Steam  had  been  used 
to  turn  a  globe  by  Hero  of  Alexandria,  a  Greek  who  lived 


246  EIGHTEENTH  CENTURY.  pt.  hi. 


1 20  years  before  Christ ;  and  Baptiste  Porta  in  1580,  Solo- 
mon de  Cans  in  1615,  and  the  Marquis  of  Worcester  in 
1663,  all  tried  to  make  use  of  steam  to  do  work.  Again,  in 
1690  and  1698,  a  Frenchman  named  Papin  and  an  English- 
man, Captain  Savery,  tried  to  make  steam-engines  to  raise 
water  out  of  mines.  But  the  only  one  of  all  these  engines 
which  we  need  describe  here  was  that  which  fell  into  the 
hands  of  Watt,  and  which  was  made  by  a  man  named  New- 
comen  in  1705.  A  plan  of  Newcomen's  engine  is  given  in 
Fig.  41.  Its  working  depended  on  the  pressure  of  the 
atmosphere  (explained  p.  123)  on  the  piston  at  one  end  of 
the  beam,  and  the  weight  of  the  lump  of  iron,  e^  at  the  other 
end. 

The  lever-beam  of  this  engine  is  balanced  in  such  a 
way  that  when  it  is  not  at  work  the  weight  e  pulls  it  down 
on  the  side  away  from  the  engine,  and  the  piston,/,/,  is  drawn 
up  to  the  top  of  the  cylinder,  as  in  the  figure.  To  set  the 
engine  going  a  fire  is  lighted  under  the  boiler,  and  the 
tap  or  stopcock,  a,  is  opened,  so  that  the  steam  rises  into 
the  cylinder,  driving  out  the  air  through  the  air- vent,  c.  As 
soon  as  the  cylinder  is  full  of  steam,  a  is  turned  off,  and  the 
stopcock,  b,  turned  on.  Immediately  a  small  jet  of  cold 
water  from  the  tank  t  rushes  through  b  into  the  cylinder, 
turning  the  steam  back  into  a  few  drops  of  water,  which  flow 
out  with  the  cold  water  down  the  pipe  d.  Now  notice,  the 
cylinder  is  quite  empty  ;  for  the  steam  drove  out  the  air,  and 
the  cold  water  carried  the  steam  away  with  it,  while  no  air  can 
come  in  at  c  or  d,  because  the  little  valves  in  them  are  kept 
shut  by  the  weight  of  the  atmosphere  outside.  So  there  is 
nothing  to  hold  up  the  piston,  which  is  being  heavily  pressed 
down  by  the  air  above  it.  The  consequence  is,  down  it 
comes  to  the  bottom  of  the  cylinder,  dragging  with  it  the 


CH.  XXVIII. 


NEWCOMEN'S  ENGINE. 


247 


end  of  the  lever-beam.  Directly  it  reaches  the  bottom 
the  stopcock  b  has  to  be  shut,  and  a  opened  again.  Up 
rises  the  steam  directly  from  the  boiler,  driving  up  the  piston, 
and  the  whole  thing  begins  again.  In  this  way  the  lever- 
beam  is  kept  moving  up  and  down  by  simply  turning  the 

Fig.  41. 


Newcomen  Engine  (Black). 

a.  Stopcock  between  boiler  and  cylinder.  3,  Stopcock  between  cold-water  tank  and 
cylinder,  c.  Valve  closing  air-vent,  d.  Valve  closing  the  outlet  for  condensed 
steam,  e.  Weight  which  drags  down  the  beam.  /,  p.  Piston  which  is  pressed 
down  by  the  atmosphere  when  the  cylinder  is  empty.' 

two  stopcocks  one  after  the  other.  These  were  at  first 
opened  and  shut  by  boys ;  but  one  day  an  ingenious  lad 
named  Humphrey  Potter,  who  wanted  to  save  himself  the 
trouble  of  turning  the  cocks,  found  that  by  tying  strings  from 


*  The  boiler  and  cold-water  tank  both  in  this  figure  and  in  fig.  43 
are  draAvn  much  too  small  in  proportion,  in  order  to  bring  them  into 
the  figure. 


248  EIGHTEENTH  CENTURY.  ft.  hi. 

the  handles  to  the  different  ends  of  the  beam  he  could  make 
the  engine  open  its  own  cocks  as  the  beam  went  up  and 
down.  This  rough  arrangement  was  soon  improved,  and 
the  machine  worked  by  itself. 

Watt's  Separate  Condenser. — Such  was  the  engine  as 
Watt  found  it.  When  he  began  to  examine  it  he  saw  at 
once  what  an  immense  quantity  of  heat  was  wasted.  Every 
time  the  piston  came  down,  the  cylinder,  as  well  as  the 
steam  in  it,  had  to  be  cooled  down  j  every  time  the  piston 
rose,  the  cylinder  had  to  be  heated  again ;  and  the  thing 
which  puzzled  him  most  about  it  was,  that  it  took  six  pounds 
of  cold  water  to  condense  only  one  pound  of  steam. 

It  was  in  this  difficulty  that  he  came  to  Dr.  Black,  and 
learnt  from  him  the  theory  of  latent  heafy  which  showed  that 
there  is  an  immense  store  of  heat  hidden  in  steam,  which 
has  to  be  drawn  out  before  it  can  become  water.  This  was 
an  entirely  new  light  to  Watt,  and  it  led  him  to  make  many 
experiments  still  more  exact  than  those  of  Dr.  Black,  which 
convinced  him  that  no  engine  would  ever  work  well  or 
economically,  while  so  much  power  was  wasted  in  cooling 
and  re-heating  the  cylinder  at  every  stroke.  But  how  was 
he  to  cool  down  the  steam  without  cooling  the  cylinder 
which  held  it  ? 

For  months  he  pondered  over  this  without  finding  any 
answer.  At  last,  one  Sunday  afternoon,  when  he  was  walk- 
ing on  the  Green  of  Glasgow,  the  way  to  do  it  flashed  upon 
his  mind.  If  he  could  draw  the  steam  off  into  a  separate  vessel 
and  condense  it  there,  the  cylinder  might  still  be  kept  hot,  a7id 
the  thing  would  he  done.  Fig.  42  will  help  you  to  understand 
how  this  could  be  effected.  Here  the  two  flasks,  a  and 
B,  are  first  quite  emptied  of  air,  and  b  is  half  filled  with 
water.     Under  b  is  placed  a  lamp,  d  ;  under  a,  a  basin  of 


CH.  XXVIII.  CONDENSATION   OF  STEAM.  249 

ice,  E.  Now  as  long  as  the  tap,  c,  is  kept  open,  the  steam 
which  is  constantly  rising  from  the  water  in  b  will  rush  along 
the  tube  into  the  empty  flask,  a,  and  will  there  be  turned  into 
drops  of  water  by  the  cold  of  the  ice  underneath,  and  this 
will  go  on  as  long  as  there  is  any  water  left  in  b,  because 
there  will  always  be  an  empty  space  or  vacuum  in  a  to  re- 
ceive the  steam  as  it  rises.  When  the  tap,  c,  is  shut,  the 
steam  in  b  will  become  very  dense,  and  when  it  is  opened 

Fig.  42. 


Steam  condensed  in  a  separate  Vessel. 

A,  Flask  empty  of  air.  B,  Flask  half-full  of  water  and  empty  of  air.  c,  Tap  con- 
necting the  two  bottles.  D,  Spirit  lamp  keeping  the  water  in  B  boiling,  e.  Basin 
of  ice  cooling  down  the  steam  which  passes  into  A. 

again  the  greater  part  of  the  steam  will  rush  out  and  be 
cooled  down  in  a,  while  b  remains  hot  as  before. 

Watt's  Engine. — This  was  exactly  the  plan  Watt  adopted 
in  his  steam-engine  ;  b  answers  to  his  cylinder  (Fig.  43), 
which  could  be  kept  always  hot,  and  a  to  his  condenser,  in 
which  his  steam  was  turned  back  into  water.  We  cannot 
follow  out  all  the  different  steps  of  his  invention,  and  must 
content  ourselves  with  a  rough  description  of  his  engine 
after  he  had  completed  it,  as  shown  in  Fig.  43. 

In  the  first  place  you  must  notice  that  cold  water  is  kept 
flowing  down  from  the  tank  a  into  b,  and  out  through  the  pipe 
C,  so  that  the  condenser  standing  inside  b  is  kept  quite  cold  : 


250 


EIGHTEENTH  CENTURY. 


FT.   III. 


and,  secondly,  I  must  tell  you  that  the  rods,  i  and  2,  are  so 
placed  that  when  the  engine-end  of  the  lever-beam  is  raised, 
as  in  the  figure,  the  stopcocks  a  and  c  are  open,  and  b  and  d 
are  shut ;  and  when  that  end  of  the  beam  falls,  b  and  d  will  be 
open,  and  a  and  c  will  be  shut. 

Let  us  now  begin  with  the  machine  as  we  see  it  in  the 
figure.  In  this  position  of  the  beam  the  cocks  a  and  c  are 
open  j  therefore,  the  steam  below  the  piston  will  rush  out  at 

Fig.  43. 

A 

COLD  WATER 


A,  B,  Cold  water  tanks.  _  c,  Outlet  for  cold  water,  d,  e,  Pumps  for  drawing  off  hot 
water  and  sending  it  along  s,  s,  back  to  the  boiler,  p.  Tight-fitting  piston. 
a,  d,  Cocks  for  letting  steam  into  the  cylinder,  b,  c.  Cocks  for  letting  steam  out 
of  the  cylinder,  e,  e,  Pipe  which  carries  steam  from  boiler  to  cylinder,  o,  o.  Pipe 
which  carries  steam  from  cylinder  to  condenser,  i,  2,  Rods  connecting  the  cocks 
with  the  lever-beam. 

c  into  the  condenser,  there  to  be  turned  into  drops  of  water, 
while  the  steam  from  the  boiler,  entering  at  «,  will  force  the 


CH.  XXVIII.  WATT'S  ENGINE.  ■  251 

piston  down.  But  now,  the  piston  having  pulled  doA\Ti  the 
beam,  a  and  c  will  be  closed  and  the  other  two  cocks,  b  and 
d,  will  be  opened.  So  the  steam  above  the  piston  will  rush 
out  at  b  into  the  condenser,  while  the  steam  from  the  boiler 
will  pass  directly  from  e  down  to  d,  and  coming  in  below  the 
piston,  will  drive  it  up  again.  In  this  way,  although  the  cylin- 
der is  never  cooled,  the  piston  moves  steadily  up  and  down ; 
because  the  steam  is  driven  off  into  the  condenser  standing 
in  B,  where  it  is  turned  into  water,  and  is  drawn  up  by  the 
two  pumps  D  and  e,  and  sent  along  the  pipe,  s,  s,  back  to  the 
boiler. 

This  was  the  principle  of  Watt's  double-acting  steam- 
engine,  and  if  you  understand  the  difference  between  Figs. 
41  and  43  you  will  see  that,  though  Watt  was  not  the  first  to 
make  engines  move  by  steam,  he  was  the  first  to  make  a 
pure  sfeatn-engme,  where  the  piston  moves  up  and  down 
without  any  help  from  the  outside  air,  or  of  the  counter- 
balancing weight  e,  Fig.  41,  and  without  the  enormous  waste 
of  heat  and  fuel  which  made  all  the  earlier  engines  com- 
paratively useless. 

I  have  only  told  you  here  of  the  way  in  which  he  applied 
steam  to  his  engines ;  all  the  numberless  other  improvements 
which  he  made  you  must  read  about  in  books  on  engineering. 
For  twenty  long  years  he  went  on  improving  and  inventing 
without  reaping  any  reward  for  his  labour.  Other  men  tried 
to  steal  his  ideas  and  to  make  a  profit  out  of  his  genius,  and 
he  had  to  fight  against  prejudice  and  injustice,  and  against 
constant  depression  caused  by  his  own  ill-health.  Yet  he 
found  many  kind  friends  upon  his  road,  and  amongst  the 
most  famous  of  these  was  Boulton,  the  Birmingham  manu- 
facturer, who  became  his  partner  in  1769,  and  stood  by  him 
manfully  in  all  his  difficulties  and  troubles.     It  was  from 


252  EIGHTEENTH  CENTURY,  pt.  hi. 

Boulton's  manufactory  at  Soho  (a  suburb  of  Birmingham) 
that  Watt's  engines  went  forth  to  the  world,  and  worked  that 
great  change  in  the  manufactures  of  England  which  has 
made  us  one  of  the  first  nations  of  the  world. 

The  names  of  Boulton  and  Watt  deserve  to  be  classed 
together  as  benefactors  of  mankind.  Watt  was  the  inventor, 
the  man  who  loved  science,  and  who  could  not  live  without 
creating.  Boulton  was  the  large-minded,  enterprising  man 
of  business  j  he  gave  Watt  men,  money,  courage,  and  sup- 
port to  carry  out  his  inventions  \  and  by  his  sympathy  with, 
and  command  over  the  workmen,  he  led  the  army  which 
conquered  indifference,  persecution,  and  difficulties,  and 
established  steam  machinery  in  all  the  workshops  of  the 
world.  Watt  died  in  1819,  in  the  eighty-third  year  of  his 
age,  and  was  buried  in  Handsworth  Church,  near  his  friend 
and  partner  Boulton,  who  had  died  ten  years  before. 


Chief  Works  consulted. — Black's  'Elements  of  Chemistry,'  1803; 
'Edinburgh  Review,' vol.  xiii.  'History  of  Steam-engines;'  Arago, 
'Biographies  of  Scientific  Men,'  1857  ;  Smiles's  'Lives  of  Boulton  and 
Watt ; '  Everett  Deschanel's  '  Natural  Philosophy  ; '  Tyndall's  '  Natural 
Philosophy ; '  Balfour  Stewart's  '  Treatise  on  Heat  j '  Beckman's  '  His- 
tory of  Inventions.* 


CH.  XXIX.  BENJAMIN  FRANKLIN.  253 


CHAPTER  XXIX. 

SCIENCE    OF   THE   EIGHTEENTH    CENTURY    (CONTINUED). 

Benjamin  Franklin,  bom  1706 — His  Early  Life— Du  Faye  discovers 
two  kinds  of  Electricity — Franklin  proves  that  Electricity  exists  in 
all  bodies,  and  is  only  developed  by  Friction — Positive  and  Nega- 
tive Electricity — Franklin  draws  down  Electricity  from  the  Sky 
— Invents  Lightning-conductors — Discovery  of  Animal  Electricity 
by  Galvani  — Controversy  between  Galvani  and  Volta  —  Volta 
proves  that  Electricity  can  be  produced  by  the  Contact  of  two 
Metals— Electrical  Batteries— The  Crown  of  Cups— The  Voltaic 
Pile. 

Benjamin  Franklin,  born  1706.-— He  Investigates  the 
Nature  of  Electricity,  1746. — Benjamin  Franklin,  the  printer 
and  man  of  science,  was  born  at  Boston,  in  America,  in  the 
year  1706.  He  was  the  son  of  a  tallow-chandler,  and  had 
so  many  hard  struggles  in  his  early  life  that  he  does  not  seem 
to  have  turned  his  thoughts  to  science  till  he  was  nearly 
forty  years  of  age.  His  father  intended  him  for  the  Church, 
but  there  was  not  enough  money  to  pay  for  his  education,  so 
he  was  apprenticed  to  his  brother,  who  was  a  printer.  Here 
he  worked  very  hard,  yet  he  used  to  snatch  every  spare 
moment  to  read  any  books  which  came  within  his  reach ; 
but  his  brother  being  unkind  and  harsh  to  him.  a  quarrel 
sprang  up  between  them,  and  Benjamin  at  last  ran  away  to 
New  York,  and  from  there  to  Philadelphia.  In  this  last 
place  he  got  a  little  work,  but  hoping  to  do  better  in 
England  he  came  to  London,  where  he  learnt  many  of  the 


254  EIGHTEENTH  CENTURY,  pt.  ill 

newest  improvements  in  printing.  After  a  time  he  went 
back  to  Philadelphia,  and  from  that  time  he  began  to  succeed 
as  a  printer  and  became  a  well-known  and  respected  man. 

It  was  in  the  year  1746  that  he  first  began  to  pay  atten- 
tion to  the  experiments  in  electricity  which  were  being  made 
in  England  and  France.  A  great  deal  had  been  learnt 
about  this  science  since  the  time  when  Otto  Guericke  made 
the  first  electrical  machine  in  1600,  and  a  Frenchman  named 
Du  Faye  had  shown  that  two  different  kinds  of  electricity 
could  be  produced  by  rubbing  different  substances.  You  will 
remember  that  a  pith-ball,  when  filled  with  electricity  from 
a  stick  of  electrified  sealing-wax,  draws  back,  and  will  not 
approach  the  sealing-wax  again  (seep.  124).  But  Du  Faye 
discovered  that  if  you  rub  the  end  of  a  glass  rod  with  silk, 
and  bring  it  near  to  this  ball,  it  will  draw  the  ball  towards 
itself,  showing  that  the  electricity  in  the  glass  rod  has 
exactly  the  opposite  effect  to  that  in  the  sealing-wax.  In 
other  words,  while  Guericke  had  shown  that  substances 
filled  with  the  saine  kind  of  electricity  repel  each  other,  Du 
Faye  showed  that  substances  filled  with  diffe7'ent  kinds  of 
electricity  attract  each  other.  Both  these  men  thought  that 
electricity  was  a  fluid  which  was  created  by  the  rubbing,  and 
which  was  not  in  bodies  at  other  times ;  when  Franklin,  how- 
ever, began  to  make  his  experiments  he  saw  clearly  that  this 
was  not  as  they  had  supposed,  but  that  all  bodies  have  more 
or  less  electricity  in  them,  which  the  rubbing  only  brings  out. 

The  way  in  which  he  proved  this  is  very  interesting ; 
but  to  understand  it  you  must  first  know  that  any  body 
which  is  to  be  filled  with  electricity  requires  to  be  so  placed 
that  the  electricity  cannot  pass  away  from  it  into  the  earth. 
The  best  way  to  do  this  is  to  stand  it  upon. a  stool  with  glass 
legs,  because  electricity  does  not  pass  easily  along  glass. 


CH.  XXIX.      EXPERIMENTS  IN  ELECTRICITY.  255 

You  must  also  know  that  when  any  substance  is  full  of 
electricity,  if  you  bring  your  finger  or  a  piece  of  metal  near 
to  it,  a  spark  will  pass  between  the  electrified  substance  and 
your  finger  or  the  metal. 

You  will   now,  I  think,  be   able  to  follow  Franklin's 
experiments.     He  put  a  person,  whom  we  will  call  a,  upon 
a  glass  stool,  and  made  him  rub  the  metal  cylinder  of  an 
electrical  machine  with  one  hand  and  place  his  other  hand 
upon  it  to  receive  the  electricity.     Now,  he  said,  if  elec- 
tricity is  created  by  the  rubbing,  this  person  must  be  filled 
with  it,  for  he  will  be  constantly  taking  it  from  the  machine, 
and  it  cannot  pass  away,  because  of  the  glass  legs  under  the 
stool.     But   he  found    that   a  had  no  more  electricity  in 
him  after  rubbing  the  cylinder  than  he  had  before,  neither 
could  any  sparks  be  drawn  out  of  him.      He   then  took 
two  people,  A  and  b,  and  placing  each  of  them  on  a  glass 
stool,  made  a  rub  the  cylinder,  and  b  touch  it,  so  as  to  receive 
the  electricity.    Now  notice  carefully  what  happened,    e  was 
soon  so  full  of  electricity  that  when  Franklin  touched  him, 
sparks  came  out  at  all  points  ;  but  what  was  still  more  curious, 
when  Franklin  went  to  A  and  touched  him,  sparks  came  out 
between  them  just  as  they  had  done  between  him  and  b. 

This  he  explained  as  follows  :  '  a,  b,  and  myself,'  he  said, 
*  have  all  our  natural  quantity  of  electricity.  Now  when  a 
rubbed  the  tube,  he  gave  up  some  of  his  electricity  to  it,  and 
this  B  took,  so  that  a  had  lost  half  his  electricity  and  b  had 
more  than  his  share.  I  then  touched  b,  and  his  extra 
charge  of  electricity  passed  into  me  and  ran  away  into  the 
earth.  I  now  went  to  a,  and  I  had  more  electricity  in  me 
than  he  had,  because  he  had  lost  half  his  natural  quantity, 
and  so  part  of  my  electricity  passed  into  him,  producinfr 
the  sparks  as  before.' 


256  EIGHTEENTH  CENTURY.  pt.  hi. 

This  Franklin  believed  to  be  the  case  with  all  electricity, 
namely,  that  every  body  contains  its  own  amount  of  it,  but 
that  when  for  any  reason  it  is  distributed  unequally,  those 
which  have  no  more  than  they  can  well  carry,  give  some  up 
to  those  which  have  less,  till  they  have  each  their  right 
quantity.  And  this  explained  at  once  why  a  man  cannot 
electrify  himself,  for  so  long  as  he  has  no  one  else  from  whom 
he  can  procure  electricity,  he  is  only  taking  back  with  one 
hand  what  he  gives  out  with  the  other.  Those  who  had  too 
much  electricity  were  called  by  Franklin  positively  electrified^ 
and  those  who  had  too  little,  negatively  electrified,  and  from 
this  come  the  terms  positive  and  negative  electricity,  which 
are  now  used. 

I  should  tell  you  here  that  it  is  now  believed  that 
electricity  is  composed  of  two  different  kinds  existing  to- 
gether in  all  substances.  These  two  kinds  are  supposed  to 
remain  at  rest  as  long  as  they  are  equally  balanced,  but 
when  a  body  contains  too  much  of  one  kind,  it  is  always 
trying  either  to  give  it  up  or  to  get  some  of  the  other  kind 
to  balance  it.  This  theory  explains  some  facts  which 
Franklin's  theory  does  not ;  but  it  is  not  yet  really  known 
what  electricity  is,  only  it  is  certain  that  Franklin  was  riglit 
in  saying  that  it  is  not  created  when  we  see  its  effects,  but 
only  drawn  out  of  bodies  which  contain  it. 

Franklin  draws  down  Lightning  from  the  Sky. — It 
was  in  1749,  when  he  had  already  made  most  of  his  experi- 
ments upon  electricity,  that  Dr.  Franklin  began  to  consider 
how  many  of  the  effects  of  thunder  and  lightning  were  the 
same  as  those  which  he  could  produce  with  his  electrical 
machines.  Lightning  travels  in  a  zigzag  line,  said  he,  and 
so  does  an  electric  spark ;  electricity  sets  things  on  fire,  so 
does  lightning ;  electricity  melts  metals,  so  does  lightning. 


CH.  XXIX.  FRANKLIN'S  KITE.  257 

Animals  can  be  killed  by  both,  and  both  cause  blindness  ; 
electricity  always  finds  its  way  along  the  best  conductor,  or 
the  substance  which  carries  it  most  easily,  so  does  lightning  ; 
pointed  bodies  attract  the  electric  spark,  and  in  the  same 
way  lightning  strikes  spires,  and  trees,  and  mountain  tops. 
Is  it  not  most  likely  that  lightning  is  nothing  more  than 
electricity  passing  from  one  cloud  to  another  just  as  an 
electric  spark  passes  from  one-  substance  to  another  ? 

Franklin  communicated  these  ideas  to  the  Royal  Society 
in  London,  suggesting  at  the  same  time  that,  if  he  was  right, 
it  would  be  possible  to  prevent  a  great  deal  of  the  harm 
done  by  lightning  by  fixing  upright  rods  of  iron  near  high 
buildings  so  that  the  electricity  might  run  down  from  the 
clouds  into  the  earth  without  doing  any  harm.  But  this 
notion  seemed  so  absurd,  even  to  clever  men,  that  they 
could  not  help  laughing  when  his  papers  were  read,  and  did 
not  even  think  them  worth  printing.  You  will  easily  un- 
derstand that  after  this  Franklin  was  ashamed  to  speak  of 
an  experiment  he  meant  to  make  by  which  he  hoped  to 
bring  down  electricity  from  the  sky.  So  we  find  that  he 
told  no  one  but  his  son,  whom  he  took  with  him  upon  this 
strange  expedition. 

Franklin's  idea  was  that  if  he  could  send  an  iron  rod 
up  into  the  clouds  to  meet  the  lightning,  it  would  become 
charged  with  the  electricity,  which  he  believed  was  there, 
and  would  send  it  down  a  thread  attached  to  it,  so  that  he 
might  be  able  to  feel  it.  He  took,  therefore,  two  light  strips 
of  cedar  fastened  crossways,  upon  which  he  stretched  a  silk 
handkerchief  tied  by  the  comers  to  the  end  of  the  cross,  and 
to  the  top  of  this  kite  he  fixed  a  sharp-pointed  iron  wire 
more  than  a  foot  long.  He  then  put  a  tail  and  a  string  to 
his  kite,  and  at  the  end  of  the  string  near  his  hand  he  tied 


258  EIGHTEENTH  CENTURY.  pt.  hi. 

some  silk  (which  is  a  bad  conductor),  to  prevent  the  elec- 
tricity from  escaping  into  his  body.  Between  the  string  and 
the  silk  he  tied  a  key,  in  which  the  electricity  might  be 
collected. 

When  his  kite  was  ready  he  waited  eagerly  for  a  heavy 
thunderstorm,  and,  as  soon  as  it  came,  he  went  out  with  his 
son  to  the  commons  near  Philadelphia  and  let  his  kite 
fly.  It  mounted  up  among  the  dark  clouds,  but  at  first  no 
electricity  came  down,  for  the  string  was  too  dry  to  conduct 
it.  But  by-and-by  the  heavy  rain  fell,  the  kite  and  string 
both  became  thoroughly  wet,  and  the  fibres  of  the  string 
stood  out  as  threads  do  when  electricity  passes  along  them. 
Directly  Franklin  saw  this  he  knew  that  his  experiment  had 
succeeded ;  he  put  his  finger  to  the  key  and  drew  out  a 
strong  bright  spark,  and  before  long  he  had  a  rapid  current 
of  electricity  passing  from  the  key  to  his  finger.  The  wise 
men  of  London  might  now  laugh  if  they  pleased,  for  the  dis- 
covery was  made  j  he  had  drawn  lightning  from  the  sky,  and 
proved  that  it  was  electricity  !  Soon  after  this  he  made  an 
apparatus  in  his  own  house  for  collecting  electricity  from  the 
clouds,  which  rang  a  peal  of  bells  when  it  was  sufficiently 
charged  for  him  to  make  experiments  with  it.  He  also 
introduced  iron  rods  as  lightning  conductors,  which  were 
for  the  future  placed  near  all  high  buildings  to  attract  the 
lightning  and  carry  it  away  into  the  ground. 

Franklin  had  now  earned  a  great  name ;  he  was  made  a 
Fellow  of  the  Royal  Society,  and  many  honours  were  paid  to 
him  by  all  the  countries  of  Europe.  He  made  many  other 
very  valuable  experiments,  and  was  besides  an  active  citizen 
and  politician.  He  died  in  1790,  in  his  eighty-fifth  year, 
after  a  life  of  hard  labour  and  toil,  for  which,  however,  he 
v/as  well  repaid  by  success. 


CH.  XXIX.  ANIMAL  ELECTRICITY.  259 

Discovery  of  Animal  Electricity  by  Galvani,  and  of 
Chemical  or  Voltaic  Electricity  by  Volta,  1789-1800.—- 

Only  a  few  months  before  Franklin  died  a  new  fact  had 
been  discovered  about  electricity,  which  would  have  given 
the  old  man  great  delight  if  he  could  have  lived  to  see  the 
results.  This  discovery  was  made  by  Galvani,  Professor 
of  Anatomy  at  Bologna,  or  perhaps  we  ought  to  say  by 
Madame  Galvani,  for  it  was  her  observation  which  first .  led 
her  husband  to  study  the  subject. 

Aloysius  Galvani  was  born  at  Bologna  in  1737,  and  we 
know  little  of  his  early  life  except  that,  instead  of  becoming 
a  monk  as  he  first  intended,  he  married  a  professor's 
daughter,  and  became  the  Lecturer  on  Anatomy  in  the 
University  of  Bologna.  He  had  in  his  house  an  electrical 
machine  which  he  used  for  experiments,  and  one  day  in 
1789,  as  Madame  Galvani  was  skinning  frogs  for  a  soup,  one 
of  Galvani's  assistants  was  working  the  machine  near  her. 
Just  as  the  flow  of  electricity  was  going  on  rapidly,  this 
.  young  man  happened  to  touch  a  nerve  of  the  leg  of  a  dead 
frog  with  a  dissecting  knife,  and  to  his  great  surprise  the  leg 
began  to  move  and  struggle  as  if  it  were  alive.  Madame 
Galvani  was  so  much  struck  by  this  that  she  told  her  hus- 
band of  it  directly  he  returned,  and  he  repeated  the  experi- 
ment many  times,  and  found  that  whenever  the  flow  of 
electricity  from  the  machine  was  brought  near  the  nerve  of 
the  frog's  leg  it  produced  convulsions.  He  next  tried 
whether  lightning  brought  down  upon  the  nerves  of  the  leg 
would  have  the  same  effect,  and  the  experiment  succeeded 
perfectly. 

Meanwhile  another  accident  showed  him  that  the  con- 
vulsions could  be  produced  without  either  lightning  or  an 
electrical  machine.     He  had  prepared   the   hind  legs   of 


26o  EIGHTEENTH  CENTURY.  it.  hi. 

several  frogs  and  hung  them  by  copper  hooks  upon  an  iron 
balcony  outside  his  house.  As  they  hung  there  the  wind 
swayed  them  to  and  fro,  so  that  the  ends  of  the  legs  touched 
the  iron  of  the  balcony;  and  every  time  they  did  so 
he  noticed  that  the  legs  were  convulsed  just  as  they  had 
been  by  the  electrical  machine  and  the  lightning.  But  this 
time  he  could  not  see  that  any  electricity  had  come  near 
them  from  outside,  so  he  supposed  that  there  must  be  an 
electric  fluid  in  the  leg  itself,  which  passed  round  every  time 
the  two  ends  of  the  leg  were  joined  by  the  metal.  These 
discoveries  of  Galvani  soon  became  spoken  of  far  and  wide 
under  the  name  of  galvanism,  and  the  supposed  fluid  was 
called  the  galvanic  fluid. 

Among  the  celebrated  men  who  were  attracted  by  this 
new  discovery  was  Alessandro  Volta,  Professor  of  Natural 
Philosophy  at  the  University  of  Pavia,  who  was  bom  at 
Como  in  1745,  and  was  at  this  time  a  well-known  naturalist. 
Not  satisfied  with  merely  reading  about  Galvani's  experi- 
ments, Volta  tried  them  himself,  and  he  began  to  suspect 
that  the  electricity  was  not,  as  Galvani  imagined,  in  the  frog's 
leg,  but  was  produced  by  the  two  metals,  copper  and  iron, 
upon  which  the  legs  had  been  hung,  and  which  were  acted 
upon  by  the  moisture  in  the  flesh. 

Then  began  a  very  famous  controversy.  Volta  insisted 
that  the  electricity  came  from  the  metals^  Galvani  that  it 
came  from  the  animal.  In  each  new  experiment  which 
Galvani  brought  forward  to  prove  his  point,  Volta  still 
showed  that  the  electricity  could  be  produced  without  the 
animal,  until  at  last  Galvani  succeeded  in  finding  a  test 
which  he  thought  must  silence  Volta  for  ever.  He  found 
that  by  laying  bare  a  "nerve  of  the  leg  of  a  frog,  called  the 
*  crural  nerve,'  and  bringing  the  end  of  it  to  the  outside  of 
the  muscles  of  the  leg,  he  could  produce  the  convulsions 


CH.  XXIX.  GALVANI  AND    VOLT  A.  '         261 

without  any  metal  at  all.  But  Volta  was  not  so  easily  con- 
vinced ;  he  still  insisted  that  it  was  the  different  fluids  and 
tissues  being  brought  together  which  caused  the  electricity, 
and  that  there  was  not  a  current  running  through  the 
animal.  At  this  point,  just  when  the  truth  would  probably 
have  been  worked  out,  Galvani  died  (in  1798),  leaving 
Volta  in  possession  of  the  field ;  and  for  twenty-eight  years 
no  more  was  heard  of  animal  electricity.  We  know  now 
that  both  the  professors  were  right.  Volta  was  right  in 
saying  that  the  convulsion  of  the  frog's  legs  on  the  balcony 
was  produced  by  the  contact  of  the  two  metals  in  con- 
nection with  a  fluid ;  while  Galvani  was  right  in  saying  that 
there  is  an  electricity  in  animals  which  acts  without  any 
other  help.  In  1826  an  Italian  named  Nobili  repeated 
Galvani's  experiment,  and  having  then  an  instrument  called 
a  galvanometer  (see  p.  351),  by  which  the  passage  of  the 
faintest  electric  current  can  be  detected,  he  proved  that 
such  a  current  does  exist  in  the  frog,  and  it  has  since  been 
found  to  be  common  to  all  animals. 

Meanwhile,  however,  Volta  had  also  made  a  very  re- 
markable discovery,  namely,  that  two  different  metals  when 
joined  together  in  contact  with  moisture,  and  separated  from 
other  substances,  produce  a  current  of  electricity.  This 
may  easily  be  tried  in  its  very  simplest  form.  If  you  take 
a  piece  of  copper  and  a  piece  of  zinc  and  put  one  above 
your  tongue  and  one  below  it,  you  will  feel  nothing  remark- 
able so  long  as  the  two  metals  are  kept  separate,  but  directly 
you  let  them  touch  each  other  at  the  ends,  a  tingling  sensa- 
tion will  pass  through  your  tongue,  proving  to  you  that  an 
electrical  current  is  passing  between  the  metals.  If  you  put 
the  zinc  under  your  upper  lip,  so  that  the  copper  may  re- 
main outside,  you  may,  perhaps,  even  see  a  slight  flash 
when  the  two  metals  meet. 


262 


EIGHTEENTH  CENTURY, 


PT.  III. 


Volta  found  not  only  that  it  was  necessary  to  have 
moisture  between  the  two  metals,  but  that  some  acid  put  in 
the  water  greatly  increased  the  strength  of  the  electricity. 
Fig.  44  shows  the  first  electric  battery  which  he  made,  and 
which  is  the  one  now  commonly  used  for  simple  experi-- 
ments.  In  this  battery  each  piece  of  zinc  is  joined  to  one 
of  copper,  and  where  the  two  are  not  united  they  are  in  the 
same  cup,  so  that  the  liquid  acts  as  a  link  to  them.  We 
know  now  what  Volta  did  not  know,  that  a  chemical  change 
is  going  on  between  the  zinc  and  the  acid  water,  which  sets 
the  action  going,  but  we  do  not  yet  know  exactly  what  the 
electricity  itself  is.     The  movement  in  Fig.  44  begins  on  the 

Fig.  44. 


Volta's  Crown  of  Cups  (Fownes). 

z,  Zinc,     c.  Copper,    a  a,  h.  Connecting  wires.    The  arrows  show  the  course  of 
the  positive  currents. 

left-hand  side  at  z.  Here  the  current^  is  set  up  by  the 
action  of  the  acid  and  water  upon  the  zinc,  and  is  passed  on 
to  the  copper,  c  j  then  along  the  wire  a,  to  the  next  z,  and  so 
on  till  it  reaches  the  last  cup,  when  it  is  carried  by  the  wire 
b  back  to  the  first  piece  of  zinc,  and  so  the  round  is  com- 
pleted. 

>  There  are  always  two  currents  passing  along  the  wire — the  positive 
current,  starting  from  the  copper  to  the  zinc,  and  the  negative  current, 
going  the  opposite  way  from  the  zinc  to  the  copper  ;  but  to  avoid  con- 
fusion, the  positive  current  is  always  called  the  current^  and  no  notice 
is  taken  of  the  other. 


CH.  XXIX. 


THE    VOLTAIC  PILE. 


263 


This  battery  is  called  the  '  Crown  of  Cups,'  but  though 
it  is  so  simple,  it  has  not  become  as  famous  as  the  second 
battery  made  by  Volta,  which  is  still  called  the  '  Voltaic 
Pile  '"(see  Fig.  45).  In  this  battery  the  metals  are  laid  one 
above  the  other,  and  have  small  pieces  of  card  or  flannel 
between  them  which  are  wetted  with  salt  and  water.  The 
battery  ends  with  a  plate  of  zinc  at  the  bottom,  and  of 
copper  at  the  top,  and  these  are  connected  by  the  wire,  a  a. 
The  action  passes  round  this  battery  just  as  it  did  through 
the  cups,  and  if  the  wire,  a  a,  is  P^^ 

cut  in  the  centre  and  tipped 
with  charcoal  (which,  being  a 
had  conductor,  causes  the  elec- 
tricity to  pass  with  difficulty), 
a  bright  stream  of  fire  will  be 
kept  up  between  the  points  as 
long  as  the  battery  is  at  work. 
Such  was  Volta's  discovery, 
and  we  owe  to  it  all  the  power- 
ful galvanic  batteries  with 
which  our  most  valuable  ex- 
periments are  now  made.  He 
completed  his  Voltaic  pile  in 
1800,  just  at  the  close  of  the 
century,  and  even  from  this  slight  sketch  you  may  see  what 
grand  strides  had  been  made  in  electricity  during  the  past 
fifty  years. 

Franklin  had  proved  the  real  action  of  electricity,  had 
shown  it  to  be  the  same  as  lightning,  and  had  brought  it 
down  from  the  sky.  Galvani  had  proved  its  existence  in 
animals,  and  led  the  way  to  Volta's  discoveries ;  and  Volta 
had  produced  it  in  enormous  quantities  by  two  metals  and 


The  Voltaic  Pile  (Fownes). 

z,  Zinc,  c,  Copper,  a,  a.  Rod  con- 
necting the  top  layer  of  copper  with 
the  bottom  layer  of  zinc. 


264  EIGHTEENTH  CENTURY,  pt.  hi. 

acidulated  water,  so  as  to  keep  up  a  constant  flow,  which 
would  travel  any  distance  so  long  as  the  circuit  was  not 
broken.  Here,  you  will  see,  was  the  first  step  towards  the 
electric  telegraph.  It  was  but  a  commencement,  anH  for 
nearly  forty  years  no  further  advance  was  made  ;  but  the 
seed  was  sown,  and  when  we  reap  the  benefits  we  must 
always  remember  the  names  of  Franklin,  Galvani,  and 
Volta,  as  the  great  pioneers  in  the  science  of  electricity. 


Chief  Works  consulted.  —  Lardner's  Cyclopedia,  '  Electricity, 
Magnetism,  and  Meteorology  ; '  *  Encyclopsedias  Britannica,*  and 
'  Metropolitana,' art.  'Electricity;'  Franklin's  *  Experiments  and  Ob- 
servations on  Electricity/  1749;  Priestley,  'On  Electricity,'  1785; 
Thomson's  *  Hist,  of  Royal  Society,'  181 2;  'Life  of  Franklin,'  by 
himself,  1833;  Bennett's  'Text-Book  of  Physiology;*  Fownes's 
•  Chemistry ; '  Wilkinson's  *  Galvanism. ' 


ciL  XXX.  BRADLEY  AND  DELISLE,  265 


CHAPTER  XXX. 

SCIENCE    OF   THE    EIGHTEENTH    CENTURY   (CONTINUED). 

Bradley  and  Delisls,  Astronomers — Aberration  of  the  Fixed  Stars — 
Nutation  of  the  Axis  of  the  Earth — Delisle's  Method  of  Measuring 
the  Transit  of  Venus — Lagrange  and  Laplace — Libration  of  the 
Moon  accounted  for  by  Lagrange — Laplace  works  out  the  Long 
Inequality  of  Jupiter  and  Saturn — Lagrange  proves  the  Stability 
of  the  Orbits  of  the  Planets — Sir  William  Herschel  constructs  his 
own  Telescopes — Discoveiy  of  a  New  Planet — Discoveiy  of  Binary 
Stars  —  Herschel  studies  Star-clusters  and  Nebulae  —  Theory  of 
Nebulas  being  matter  out  of  which  Stars  are  made — The  Motion  of 
our  Solar  System  through  Space — Weight  of  the  Earth  determined 
by  the  Schehallien  Experiment — Summary  of  the  Science  of  the 
Eighteenth  Century. 

Astronomical  Labours  of  Bradley  and  Delisle. — And 
now,  as  we  approach  the  end  of  the  eighteenth  century,  w^e 
must  take  up  once  more  the  history  of  Astronomy,  which  we 
have  neglected  since  Newton  died  in  1727.  Since  that 
•  time  many  good  astronomers  had  been  occupied  in  making 
different  observations,  but  the  only  two  who  need  be  men- 
tioned were  Bradley,  the  Astronomer- Royal  (bom  1692,  died 
1762),  and  Delisle  (born  1688,  died  1768). 

Bradley  explained  two  difficult  astronomical  problems ; 
the  first  of  these  is  called  the  *  aberration  of  the  fixed  stars,' 
which  is  an  apparent  movement  of  each  fixed  star  in  a  small 
circle  in  the  heavens,  but  which  is  really  the  combined 
effect  of  the  yearly  motion  of  our  own  earth,  and  of  the  time 
which  light  occupies  in  coming  down  from  the  stars  to  us. 
13 


266  EIGHTEENTH  CENTURY.  pt.  hi. 

This  question  is  very  difficult,  as  is  also  his  second  discovery 
of  the  nutation^  or  slight  oscillation,  of  the  earth's  axis  j  but 
it  is  necessary  to  bear  in  mind  that  he  made  these  obser- 
vations, for  they  are  very  important  in  astronomy. 

Delisle  will  interest  you  because  he  proposed  a  second 
method  of  measuring  the  transit  of  Venus,  which  is  now 
used  at  stations  where  Halley's  rule  (see  p.  i6o)  cannot  be 
applied.  Delisle's  method  consists  in  marking  the  time  at 
which  the  transit  is  seen  to  begin  in  one  part  of  the  world, 
and  to  end  in  another ;  instead  of  measuring,  as  Halley  did, 
the  duration  or  length  of  time  occupied  by  the  whole  tran- 
sit as  seen  at  each  place.  It  requires  that  the  clocks  of  all 
the  different  stations  from  which  the  transit  is  observed 
should  be  set  exactly  to  the  same  time,  and  then  it  answers 
as  well  as  Halley's. 

These  discoveries  are  all  that  need  be  mentioned  during 
the  first  half  of  the  eighteenth  century,  but  during  that  time 
there  had  been  bom  within  a  few  years  of  each  other  three 
men,  Lagrange,  Laplace,  and  Herschel,  who  were  to  light  up 
the  close  of  the  century  with  the  most  brilliant  discoveries. 
The  two  first  of  these  were  Frenchmen,  the  last  we  may  fairly 
claim  as  an  Englishman  j  for  though  he  was  born  at  Hanover 
in  1738,  of  German  parents,  still  Sir  William  Herschel  came 
over  to  England  at  the  age  of  twenty-one,  and  all  his  dis- 
coveries were  made  here.  It  was  our  King  George  III.  who 
gave  him  the  pension  which  enabled  him  to  devote  himself 
to  science;  and  his  son  Sir  John  Herschel  was,  like  his 
father,  one  of  our  greatest  astronomers,  and  made  England 
his  home  and  country. 

Lagrange  and  Laplace. — Louis  de  Lagrange  was  born 
at  Turin  in  1736.  His  father,  who  had  been  Treasurer  of 
War,  lost  all  his  fortune  when  his  son  was  quite  a  child,  and 


CH.  XXX.  LAGRANGE  AND  LAPLACE.  267 

Lagrange  often  said  that  it  was  partly  owing  to  this  mischance 
that  he  became  a  mathematician.  His  talent  showed  itself 
so  early  that  before  he  was  twenty  he  was  appointed 
Professor  of  Mathematics  in  the  Military  College  of  Turin, 
where  nearly  all  his  pupils  were  older  than  himself  From 
there  he  went  to  the  Academy  of  Sciences  at  Berlin,  and 
remained  twenty  years,  during  which  time  he  worked  out 
most  of  his  celebrated  problems.  In  1787  he  settled  in 
Paris,  where  he  died  in  18 13,  at  the  age  of  seventy- seven. 

Pierre  Simon  Laplace  was  the  son  of  a  farmer,  and  was 
born  at  Beaumont-en- Auge,  near  Honfleur,  in  1749.  He, 
too,  began  work  very  early  in  life,  foi:  in  1769  the  famous 
geometer  D'Alembert  was  so  struck  with  his  talents  that  he 
procured  for  him  the  chair  of  Mathematics  in  the  Military 
School  of  Paris,  and  from  that  time  for  more  than  fifty  years 
Laplace  devoted  himself  to  the  pursuit  of  science,  never 
letting  his  active  life  as  a  politician  interfere  mth  his 
scientific  studies.     He  died  in  1827. 

The  work  which  was  done  both  by  Lagrange  and  Laplace 
in  astronomy  was  purely  mathematical,  and  dealing  as  it  did 
with  some  of  the  most  complicated  movements  of  the 
heavenly  bodies,  it  cannot  be  rightly  understood  by  any  but 
mathematicians.  But  some  general  idea  may  be  formed  of 
the  problems  they  solved,  and  we  will  take  these  in  the 
order  of  time,  for  they  treated  so  much  of  the  same  questions, 
one  taking  up  the  subject  where  the  other  left  it,  that  it  is 
difficult  to  separate  their  work. 

Libration  of  the  Moon  accounted  for  by  Lagrange, 
1764r-1780. — Long  before  the  time  of  Lagrange  it  had  been 
known  from  observation  that  the  moon  always  turns  the 
same  side  of  her  globe  towards  our  earth  as  she  goes  round 
it,  so  that  we  never  see,  and  never  can  see,  more  than  one 


268  EIGHTEENTH  CENTURY.  pt.  hi. 

side  of  her  surface,  so  long  as  she  has  the  same  movement 
as  at  present. 

In  1764  the  Acaddmie  des  Sciences  offered  a  prize  for  a 
complete  explanation  of  this  curious  fact,  and  Lagrange  was 
thus  led  to  study  the  question,  which  he  solved  quite  satis- 
factorily in  1780. 

Many  people  find  it  very  difficult  to  understand  how  the 
moon  can  be  always  turning  round  upon  her  own  axis,  as  a 
top  spins,  and  yet  always  keep  the  same  side  towards  us ; 
therefore,  it  will  be  as  well  to  make  a  simple  experiment 
which  explains  it  quite  clearly.  Take  a  round  ball  and  stick 
a  pin  in  one  side  of  it,  then  turn  the  ball  slowly  round  like  a 
teetotum,  and  notice  as  it  goes  round  that  the  pin  points 
successively  to  each  of  the  sides  of  the  room  one  after  the 
Pj^    g  other;  then  sew  a  piece  oi 

cotton  to  the  side  of  the  ball 
opposite  the  pin,  and  fasten 
the  other  end  down  to  the 

Diagram  showing  why  one  side  of  the    table  (aS  at  E,  Fig.  46).    If  yOU 
Moon  is  always  turned  towards  the 

Earth.  now  Toll  the  ball  round  the 

'''' ?epJi?ndX"the^centS^^^  table,  you  wiU  obscrvc  that 

i>,  Pin  to  mark  the  side  of  the  moon     . ,  •  •    ,       ,  i       •  j         r 

which  is  never  turned  towards  the    the  pm  pomtS   tO  Cacll  Side    01 
earth.  .-,  .  ... 

the  room  m  succession,  as  it 
did  before,  showing  that  it  has  been  turning  slowly  once 
upon  its  own  axis  while  going  once  round  the  point  e,  and 
that,  for  this  reason,  the  same  side  has  been  facing  e  all  the 
time. 

This  is  the  case  with  the  moon  as  she  travels  round  our 
earth,  and  Lagrange  proved  mathematically  that  it  must  be 
so,  as  Newton  had  already  suggested,  on  account  of  the  at- 
traction of  the  earth  upon  the  bulge  at  the  moon's  equator. 
But  Lagrange  also  showed  that  as  the  moon  moves  in  an 


CH.  XXX.         ORBITS  OF  JUPITER  AND  SATURN.  269 

ellipse  round  the  earth,  and  therefore  goes  at  one  time  a 
little  faster,  and  at  another  a  little  slower,  while  her  rotation 
on  her  own  axis  does  not  vary,  she  doss  not  keep  always 
exactly  the  same  face  towards  us,  but  we  catch  little  glimpses 
farther  round  her  globe,  sometimes  on  one  side  and  some- 
times on  the  other.  This  balancing  movement  is  called  the 
llbration  of  the  moon. 

Laplace  works  out  the  Long  Inequality  of  Jupiter  and 
Saturn,  1774-1783. — The  next  calculation  about  the  planets 
was  made  by  Laplace,  and  is  more  difficult  to  understand. 
You  will  remember  that  Newton  showed  that  every  planet^ 
attracts  every  other  planet,  and  has  some  effect  upon  its  path 
round  the  sun.     Now  it  had  been  found  by  comparing  old 
astronomical    tables  with    later   ones   that   these   different 
attractions  had  altered  some  of  the  ellipses  in  which  the 
planets  move  ;  and  both  Lagrange  and  a  celebrated  mathe- 
matician named  Euler  had  tried  to  calculate  these  changes 
and  find  out  whether  the  planets  would  ever  come  back  into 
their  old  places.     Laplace,  however,  carried  the  calculation 
farther  than  either  Lagrange  or  Euler  had  done,  and  he 
showed  that  the  whole  machinery  does  work  round  in  the 
course  of  a  long  period.     Only  two  planets,   Jupiter  and 
Saturn,  did  not  seem  to  follow  this  general  law,  but  behaved 
in   a  very  eccentric  manner;  for  it  appeared   that   during 
the   seventeenth  century  Jupiter  had    been  moving  more 
quickly  every  year  and  Saturn  more  slowly.     If  this  went  on 
it  was  clear  that  Jupiter  would  draw  nearer  to  the  sun,  and 
at  last  fall  into  it,  while  Saturn  would  go  farther  off,  and  dis- 
appear entirely  from  our  system,  and  this  would  upset  the 
balance  of  our  planets,  and  might  lead  eventually  to  our 
being  all  drawn  into  the  sun. 

This  v/as  a  very  serious  question,  and  it  was  a  grand  step 


270  EIGHTEENTH  CENTURY.  pt.  hi. 

when  Laplace  answered  it,  and  showed  that  there  was  no- 
thing to  fear,  for  that,  odd  as  their  movements  appeared, 
these  two  planets  really  obeyed  the  law  of  gravitation,  and 
would  return  to  their  old  places  like  the  other  planets  after  an 
immensely  long  period.  He  showed  that  their  irregularity 
arises  from  the  fact  that  Jupiter  travels  two-and-a-half  times 
round  the  sun  while  Saturn  travels  once,  and  on  this  account 
Jupiter  is  always  catching  Saturn  up,  so  that  the  two  planets 
are  often  near  together,  or  in  conjunction^  as  it  is  called. 
When  this  happens,  they  pull  each  other  so  strongly  that 
they  are  drawn  each  out  of  its  proper  path.  If  they  always 
met  in  the  same  places,  and  so  were  pulled  in  exactly  the 
same  direction,  they  would  never  right  themselves  again ; 
but  as  Jupiter  does  not  quite  make  three  rounds  while  Saturn 
makes  one,  their  points  of  meeting  vary  a  little  each  time, 
and  this  brings  them  round  at  last  to  their  old  positions. 
Laplace's  calculation  of  this  movement  is  called  the  long 
inequality  of  Jupiter  and  Saturn. 

Laplace  also  discovered  the  reason  why  the  moon  goes  on 
for  a  long  time  moving  more  and  more  quickly  round  our 
earth,  and  then  gradually  more  and  more  slowly.  This  pro- 
blem, which  is  too  long  to  examine  here,  was  the  last  which 
remained  to  complete  the  proof  that  Newton's  theory  of 
gravitation  would  account  for  all  the  movements  of  the 
heavenly  bodies. 

Xagrange  proves  the  Stability  of  the  Orbits  of  the 
Planets,  1776. — And  now,  in  the  year  1776,  came  Lagrange's 
great  conclusion.  He  and  Laplace  had  worked  hand  in  hand, 
proving  more  and  more  at  every  step  how  beautifully  all  the 
heavenly  bodies  move  in  order,  so  that  an  equal  balance  is 
preserved  between  them  all.  At  last  Lagrange,  taking  up 
all  the  known  facts  and  uniting  them  in  one  grand  mathe- 


CH.  XXX.  SIJ?   WILLIAM  HERSCHEL.  271 

matical  problem,  proved  that  whatever  might  be  the  changes, 
and  they  are  almost  infinite,  caused  by  all  the  attractions  of 
the  different  planets  on  each  other,  yet  in  the  course  of  long 
ages  every  part  of  the  solar  system  remains  stable.  Each 
planet  has  its  appointed  road,  along  which  it  travels,  through 
many  twists  and  turnings,  but  from  which  it  cannot  escape, 
for  the  grand  force  of  gravitation  holds  them  all  in  one 
eternal  round  about  their  sun. 

These  are  some  of  the  problems  solved  by  Lagrange  and 
Laplace.  You  cannot  expect  to  understand  their  full  signi- 
ficance, nor  must  you  imagine  that  these  few  pages  contain 
more  than  a  very  small  fraction  of  the  work  which  these  two 
mathematicians  accomplished.  Laplace  made  some  beau- 
tiful calculations  explaining  the  theory  of  the  tides,  and  you 
will  also  often  hear  him  mentioned  as  the  author  of  the 
*  Nebular  Hypothesis,'  by  which  he  taught  that  our  earth 
and  all  the  planets  were  in  the  beginning  formed  by  the 
condensation  of  gases  and  fluid  matter.  All  this,  which  is 
too  difficult  to  enter  upon  here,  is  discussed  in  his  famous 
work,  the  'Mecanique  Celeste,'  published  in  1799.  But 
the  main  points  to  be  remembered  are  that  Lagrange 
and  Laplace  proved  the  regular  order  of  the  movements  of 
the  planets,  and  explained  all  those  anomalies  which  had 
seemed  to  be  out  of  harmony  with  Newton's  theory  of  gra- 
vitation. 

Sir  William  Herschel  constructs  Ms  own  Telescopes, 
and  discovers  XJranus,  1781. — ^A\''illiam  Herschel,  who  was 
born  in  1738,  was  one  often  children.  His  father,  who  was 
an  eminent  musician,  brought  him  up  to  follow  his  own 
profession,  and  when  William  came  over  to  England  with 
his  regiment  he  started  in  life  as  a  teacher  of  music.  The 
first  three  years  in  this  country  were  years  of  hard  struggle 


272  EIGHTEENTH  CENTURY.  ft.  ill. 

and  privation,  but  at  last  he  was  appointed  organist  at  Hali- 
fax in  Yarkshirej  and  from  there  he  went  in  1766  to  Bath, 
where  he  soon  became  known  as  a  talented  musician,  play- 
ing in  the  Octagon  Chapel  and  at  concerts  and  parties  with 
immense  success,  and  procuring  a  large  number  of  private 
pupils. 

It  was  at  this  time,  in  the  midst  of  active  work  which 
kept  him  fully  occupied  all  the  day,  that  Herschel  began 
those  nightly  observations  which  have  made  his  name  famous. 
His  interest  was  at  first  excited  by  seeing  the  stars  through 
a  small  telescope  only  two  feet  in  length  j  and  his  desire  was 
so  great  to  be  able  to  penetrate  farther  into  the  starry  depths, 
that  he  sent  to  London  to  order  a  large  telescope.  When 
the  answer  came,  however,  he  found  that  the  price  of  the 
instrument  was  quite  beyond  his  means  j  and  so  determined 
was  he  to  carry  out  his  project,  that  he  set  to  work  to  con- 
struct a  telescope  with  his  own  hands.  The  first  one  an- 
swered so  well  that  he  made  several  others,  and  at  last 
succeeded  in  completing  one  forty  feet  long. 

From  that  time  he  spent  the  greater  part  of  every  night 
in  observing  the  stars,  and  on  March  13,  1781,  when  he  was 
examining  some  near  the  constellation  Gemini,  or  the 
'  Twins,'  he  caught  sight  of  one  star  more  conspicuous  than 
those  around  it.  Struck  by  its  size,  he  put  a  stronger  mag- 
nifying power  on  to  his  telescope,  and  found  to  his  surprise 
that  this  star  became  larger,  while  those  round  it  remained 
as  small  as  before.  The  fixed  stars,  as  you  know,  are  so  far 
off  that  no  magnifying  power  makes  any  difference  in  their 
apparent  size  ;  so  Herschel  began  to  suspect  that  this  must 
be  a  body  very  much  nearer  to  our  earth  than  the  stars  which 
surrounded  it.  This  led  him  to  watch  it,  and  he  soon  found 
that  instead  of  being  fixed  it  moved  onwards  steadily.     He 


CH.  XXX.  THE  PLANET  URANUS.  273 

thought  at  first  that  he  had  discovered  a  comet,  but  it  was 
not  long  before  his  wandering  star  was  proved  to  be  a  new 
planet,  moving  round  the  sun  outside  Saturn.  This  planet 
is  about  half  the  size  of  Saturn,  and  takes  more  than  eighty- 
four  years  to  go  once  round  the  sun.  It  was  first  called  the 
'  Georgian  star,'  after  George  III. ;  then  it  was  called  '  Her- 
schel,'  after  its  discoverer;  and  lastly  it  received  the  name 
Uranus,  which  it  still  retains.  It  was  through  this  discovery 
that  Herschel  became  known,  and  George  III.  gave  him  a 
pension  of  300  guineas  a  year,  and  a  house  near  Windsor, 
in  order  that  he  might  devote  himself  entirely  to  astronomy. 

Star-gauging  and  Discovery  of  Binary  Stars,  1781- 
1802. — One  of  the  first  tasks  which  Herschel  undertook,  was 
to  divide  the  stars  into  groups,  according  to  their  bright- 
ness. Thus  he  classed  the  most  brilliant  as  stars  of  the 
first  magnitude,  those  a  Httle  less  briUiant  as  of  the  second 
magnitude,  and  so  on.  While  he  was  thus  gauging^  or 
measuring  the  distance  of  the  stars  by  the  intensity  of  their 
light,  his  attention  was  arrested  by  some  which  appear 
single  when  seen  through  a  small  telescope,  but  which  prove 
to  be  two  stars  when  they  are  greatly  magnified.  A  few  of 
these  double  stars  were  known  already  when  Herschel  began 
to  observe  them,  but  he  soon  detected  no  less  than  500 
scattered  about  in  different  parts  of  the  sky. 

Now  it  had  always  been  believed  that  these  stars  ap- 
peared close  together  because  one  was  almost  directly  behind 
the  other  a  long  way  off,  just  as  two  posts  standing  one  at 
some  distance  behind  the  other  will  appear  to  touch  if  they 
are  nearly  on  a  line  with  your  eye.  But  this  explanation  did 
not  satisfy  Herschel,  for  he  observed  that  many  of  these  stars, 
instead  of  merely  passing  to  and  fro  in  a  straight  line  across 
each  other,  as  they  would  appear  to  do  in  consequence  of 


274  EIGHTEENTH  CENTURY.  pt.  III. 

the  movement  of  our  earth  in  its  orbit,  had  another  pecuHar 
curved  motion,  as  if  they  were  both  moving  round  some  point 
half-way  between  them.  This  movement  was  so  slow  that  it 
was  twenty-five  years  before  he  could  be  sure  about  it ;  but  at 
the  end  of  this  time  he  was  able  to  tell  the  Royal  Society 
that  these  double  or  binary  stars,  as  they  are  called,  are  not 
one  behind  the  other,  but  are  actual  pairs  of  stars  moving 
round  and  round  each  other,  as  if  they  were  connected  by  a 
rod  suspended  by  its  centre,  and  then  set  revolving ! 

To  understand  how  great  a  discovery  this  was,  it  is  neces- 
sary to  bear  in  mind  that  Newton  had  only  been  able  to 
prove  that  gravitation  acts  between  the  sun  and  the  planets ; 
but  here  was  a  reason  for  believing  that  even  in  the  far-off  stars, 
miUions  of  miles  away  from  our  system,  the  same  force  is 
holding  distant  suns  together,  and  keeping  them  in  their 
orbits.  This  great  discovery  has  been  still  more  clearly 
proved  by  later  investigations,  and  groups  of  two,  three,  and 
even  more  stars  are  now  known,  in  which  these  bodies  re- 
volve round  a  common  centre,  held  together  by  the  force 
of  gravitation. 

Herschel  studies  Star-clusters  and  Nebulae,  1786. — The 
next  discovery  which  Herschel  made  was  quite  as  remark- 
able as  that  of  the  binary  stars.  As  long  ago  as  the  time  of 
Ptolemy  (loo  B.C.)  five  curious  stars  had  been  observed, 
which  he  called  *  cloudy  stars,'  because  they  looked  as  if 
they  were  covered  by  a  mist ;  and  the  number  of  these 
cloudy  masses  had  been  increased  by  different  astronomers 
as  time  went  on.  When  Herschel  turned  his  attention  to 
them  he  discovered  so  many  that,  in  1786,  he  published  a 
catalogue  of  no  less  than  a  thousand,  and  added  fifteen  hun- 
dred more  a  few  years  later  !  Some  of  these  bodies,  such  as 
the  bright  spot  called  the  'beehive,'  in   the   constellation 


CH.  XXX.         STAR-CLUSTERS  AND  NEBULA.  275 

Cancer,  were  simply  clusters  of  stars  which  might  be  seen 
distinctly  through  a  telescope.  In  others  the  separate 
stars  couTd  not  be  seen  even  with  the  strongest  magnifying 
power,  but  the  group  looked  so  much  more  distinct  through 
a  powerful  telescope  than  through  a  feeble  one,  that  it  seemed 
most  likely  the  stars  were  there,  if  only  they  could  be  dis- 
tinguished. But  a  third  set  of  cloudy  bodies  did  not  appear 
in  the  least  more  separated,  even  with  the  largest  telescopes, 
and  these  Herschel  called  nebulcE,  or  clouds,  because  he 
believed  they  were  made  up  of  mere  masses  of  matter  which 
had  not  yet  formed  themselves  into  stars. 

It  was  at  this  point  that  the  grand  thought  forced  itself 
upon  his  mind  that  in  these  nebulae  we  might  be  looking 
at  the  actual  beginning  of  new  worlds  :  and  that  the  creation 
of  the  different  bodies  of  the  universe  was  not  begun  and 
finished  long  ages  ago,  but  is  even  now  going  on  under 
our  eyes.  The  nebulae  he  believed  to  be  composed  of  star- 
matter,  out  of  which  stars  might  be  slowly  forming,  so  as  to 
be  first  seen  scattered  like  minute  points  in  some  of  the  more 
hazy  star-clusters,  and  then  clearly  visible,  as  in  the  '  bee- 
hive '  in  the  constellation  Cancer.  In  those  days  Herschel 
could  get  very  few  astronomers  to  believe  in  this  idea,  but  ^ 
you  will  see  in  the  history  of  the  nineteenth  century  how  the 
discoverers  of  the  spectroscope  (seep.  327)  have  proved  that 
some  of  the  nebulae  are  made  of  gaseous  matter ;  so  that  it 
becomes  extremely  probable  that  Herschel  was  right,  and 
that,  in  far  distant  space,  star-mist  is  forming  into  stars,  and 
creating  new  suns  to  illuminate  the  universe. 

The  Motion  of  our  Solar  System  through  Space,  1783. 
— The  third  and  last  theory  which  we  can  mention  as  coming 
from  Sir  William  Herschel  is  that  of  the  motion  of  our  sun 
through  space.      In  1783  he  showed  from  a  study  of  the 


276  EIGHTEENTH  CENTCTRY,  pt.  in. 

astronomical  catalogues  of  past  centuries  that  the  stars  do 
not  stand  in  exactly  the  same  places  with  regard  to  us  as 
they  did  in  ages  gone  by,  and  that,  therefore,  either  we  or 
they  must  be  moving  through  space.  Now,  when  everything 
around  you  appears  to  be  moving  backwards,  it  is  most 
likely,  to  say  the  least,  that  it  is  you  who  are  moving  forw^ards, 
and  not  that  all  other  things  are  in  motion ;  therefore  Her- 
schel  concluded  that  the  reason  of  the  apparent  change  in 
the  place  of  the  stars  was  the  real  movement  of  our  sun  and 
its  planets  among  them. 

But,  if  such  were  the  case,  then  there  ought  to  be 
one  point  straight  in  front  of  our  path  which  would  not 
appear  to  move ;  for  if  you  walk  into  a  forest  you  will 
observe  that  the  trees  on  either  side  appear  to  spread  farther 
and  farther  apart  as  you  approach,  but  that  those  exactly  in 
front  of  you  will  not  seem  to  change  their  places.  Now 
Sir  W.  Herschel  found  one  point  in  the  sky,  in  the  con- 
stellation Hercules,  where  the  greater  number  of  the  stars 
do  not  appear  to  move,  while  those  to  the  right  and  the 
left  seem  to  be  gliding  off  each  in  their  own  direction.  He 
therefore  concluded  that  our  sun  is  carrying  the  earth  and 
the  other  planets  straight  towards  this  point  in  the  con- 
*stellation  Hercules.  The  rate  at  which  this  movement 
goes  on  is  not  accurately  known,  but  it  must  be  very 
great,  probably  at  least  as  much  as  150,000,000  miles  every 
year. 

And  here  we  must  leave  the  discoveries  of  this  great 
astronomer,  although  we  have  only  glanced  at  them  very 
superficially.  The  immense  strides  in  astronomy  made  by 
Laplace,  Lagrange,  and  Herschel  cannot  be  understood  in  a 
moment ;  and  I  wish  you  always  to  remember  that  you  can 
only  gather  crumbs  of  knowledge  from  this  book,  which 


CH.  XXX.        THE  DENSITY  OF  THE  EARTH.  277 

may,  I  hope,  lead  you  to  long  and  seek  for  more  solid 
food.  Before,  however,  we  take  leave  of  Sir  W.  Herschel, 
we  must  not  forget  to  mention  the  faithful  assistant  who 
was  so  great  a  help  to  him  in  his  labours. 

Wlien  George  III.  gave  Herschel  his  home  and  pension, 
the  astronomer  sent  to  Hanover  for  his  sister  Caroline,  and 
she  lived  with  him  and  received  a  small  salary  as  his  assist- 
ant. She  shared  his  night-watches  and  mapped  down  the 
stars,  star-clusters,  and  nebulae,  as  he  came  across  them  with 
his  slowly-moving  telescope ;  she  helped  to  draw  up  his 
catalogues,  to  write  his  papers,  and  to  make  his  calculations. 
In  a  word,  she  fulfilled  one  of  the  highest  duties  of  a  woman, 
in  becoming  the  patient  helpmate  of  a  great  and  noble  mind ; 
and  for  this  reason  although  she  never  sought  fame  for  her- 
self, the  name  of  Caroline  Herschel  will  always  be  associated 
with  the  labours  of  our  great  astronomer.  Sir  William  died 
in  1822,  in  his  eighty-fourth  year,  leaving  behind  him  a  son, 
the  late  Sir  John  Herschel,  who  will  be  mentioned  in  the 
next  chapter. 

Determination  of  the  Density  of  the  Earth  by  the  Sche- 
hallien  Experiment,  1774. — ^After  speaking  of  the  wonders 
of  the  vast  universe,  and  of  suns  so  distant  that  we  cannot 
even  guess  at  the  space  which  lies  between  them  and  us,  we 
must  now  come  back  to  our  little  planet  and  mention  a  re- 
markable experiment  which  was  made  in  1774  by  Maskelyne, 
who  was  then  Astronomer- Royal  of  England.  This  was  the 
finding  out  of  the  weight  of  the  earth  compared  to  its  size, 
or  in  other  words,  the  density  of  the  earth. 

If  our  globe  were  made  of  one  material,  it  would  be  easy 
to  weigh  a  small  piece  and  multiply  that  by  the  size,  which 
we  know  pretty  accurately,  and  so  to  get  at  the  weight  of  the 
whole.     But  as  the  rocks  of  the  earth's  crust  differ  very  much 


278  EIGHTEENTH  CENTURY^  PT.  in. 


in  weight,  and  we  do  not  know  what  the  middle  of  the  globe 
is  made  of,  this  plan  is  not  possible.  We  know,  however, 
that  every  atom  of  matter  has  the  power  of  attraction,  so 
that  if  we  could  find  out  how  much  attraction  our  earth  pos- 
sesses, by  comparing  it  with  the  attraction  of  some  other 
body  which  we  can  weigh,  then  we  could  arrive  at  the  weight 
of  the  earth. 

Now  Newton,  in  his  *  Principia,'  had  pointed  out  that  a 
plumb-line,  that  is,  a  piece  of  string  with  a  weight  of  lead  at 
the  end  of  it,  will  not  point  straight  to  the  centre  of  the 
earth  when  it  is  held  near  a  mountain,  because  the  mountain 
attracts  the  lead  and  draws  it  slightly  towards  itself.  There- 
fore, if  the  size  and  weight  of  the  mountain  were  known,  and 
it  were  also  known  how  great  its  pull  is  compared  to  the 
pull  of  the  whole  earth,  this  would  enable  a  mathematician 
to  calculate  the  weight  of  our  entire  globe. 

A  man  named  Bougler  was  the  first  to  make  this  experi- 
ment near  a  high  mountain  in  Peru  in  1738,  but  he  suc- 
ceeded very  imperfectly,  and  in  1772  Maskelyne  proposed 
to  the  Royal  Society  to  repeat  the  observation.  Accord- 
ingly, he  went  in  1774  to  a  very  high  mountain  called  Sche- 
hallien,  near  Loch  Tay,  in  Perthshire,  and  there  he  measured 
the  inclination  or  slope  of  the  plumb-line  on  each  side  of 
the  mountain.  You  will  remember  that,  according  to  the 
theory  of  gravitation,  the  lead  at  the  end  of  the  line  would 
point  straight  to  the  centre  of  the  earth  c  if  the  mountain 
did  not  disturb  it  \  ^  and  if  the  plumb-line  is  taken  to  two 
places  a  certain  distance  apart  and  its  inclination  measured 
by  means  of  one  of  the  stars  overhead,  it  is  easy  to  find  out 

•  This  is  not  strictly  true,  on  account  of  bulge  at  the  equator  and 
flattening  of  the  poles ;  but  the  discrepancy  is  of  no  importance  to  the 

argument. 


CH.  XXX.      THE  SCHEHALLIEN  EXPERIMENT. 


279 


Fig.  47. 


exactly  how  much  the  lines  d  f  will  slope  towards  each 
other  when  no  mountain  is  between  them.  This  measure- 
ment being  known,  Maskelyne  then  made  two  observations, 
one  on  each  side  of  Schehallien,  and  found  that  in  this  case 
the  inclination,  instead  of  being  from  d  to  f  on  each  side, 
was  from  e  to  f,  because  the  mountain  drew  the  lead  towards 
itself  on  either  side.  So  the  deflection  e  f  d  through  which 
the  plumb-line  was  drawn 
from  the  perpendicular  showed 
the  difference  between  the  pull 
of  the  whole  earth  and  the  pull 
of  the  mountain. 

Then  Dr.  Hutton,  the  cele- 
brated geologist,  set  to  work 
to  find  out  the  size  and  weight 
of  Schehallien.     This  he  did 
by  surveying  it  and  measuring 
it  in  every  direction,  and  then 
taking  pieces  of  the  different 
rocks  it  contained  and  weigh- 
ing   them    carefully.      When 
this  was   done  it  was   found 
that  the  mountain  pulled  half 
as  strongly  in  comparison  to 
its  size  as  the  earth  did  for  its 
size.     This  showed  that  the  materials  in  the  mountain  were 
half  as  heavy  as  the  average  of  those  in  the  earth  generally, 
and  as  they  were  also  about  2  J  times  as  heavy  bulk  for  bulk 
as  water  it  was  proved  that  the  whole  globe  is  about  five 
times  heavier  than  it  would  be  if  it  was  made  entirely  of  that 
fluid. 


Schehallien  Experiment  for  estimating 
the  Density  of  the  Earth  (Herschel). 

A  B,  Surface  of  the  earth,  d,  c,  d,  Angle 
formed  by  the  two  plumb-lines  point- 
ing to  the  centre  of  the  earth. 
E,  G,  E ,  Angle  formed  by  the  two 
plumb-lines  when  drawn  aside  by  the 
mountain  M. 


This  calculation  must  be  very  near  the  truth,  for  the 


28o  EIGHTEENTH  CENTURY.  pt.  hi. 

chemist  Cavendish  obtained  nearly  the  same  result  from 
quite  a  different  experiment  made  with  a  pendulum.  This, 
which  is  called  the  '  Cavendish  experiment,'  is  too  difficult  to 
explain  here.  In  our  own  times.  Sir  Henry  James,  Sir 
Edward  Sabine,  and  others,  have  repeated  these  observations 
and  found  them  to  be  correct. 

Summary  of  tlie  Science  of  the  Eighteenth  Century. — 

This  sketch  of  the  advance  of  astronomy  brings  us  to  the 
end  of  the  science  of  the  eighteenth  century  ;  for  although 
the  greater  number  of  the  eminent  scientific  men  of  our  day 
were  bom  before  the  year  1800,  yet  their  works  belong 
chiefly  to  the  nineteenth  century.  Before  going  farther 
therefore  we  must  now  look  back  and  see  how  far  science 
has  travelled  since  our  summary  of  the  seventeenth  century. 
Biology,  or  the  science  of  life,  had  made  great  progress. 
It  had  been  enriched  by  the  study  of  organic  chemistry., 
founded  by  Boerhaave,  by  which  we  learn  the  elements  of 
which  living  bodies  are  composed  ;  by  a  more  complete 
knowledge  of  anatomy,  or  the  structure  of  the  body  in  all 
its  most  minute  parts,  as  Haller  studied  and  represented 
them  in  his  anatomical  works  j  and  by  a  knowledge  of 
comparative  anatomy,  as  taught  by  John  Hunter ;  or  the  Com- 
parison of  each  organ  as  it  appears  in  different  beings,  from 
the  lowest  animal  up  to  man.  But  even  now  the  chief  point 
remains  to  be  mentioned,  for  all  these  are  of  little  use  with- 
out the  study  of  physiology,  or  the  science  of  living  beings, 
in  which  we  must  not  only  learn  the  great  facts  of  the  work- 
ing of  our  own  bodies  and  those  of  animals,  but  must  take 
into  account  the  strange  freaks  of  nature  taught  us  by  the 
experiments  of  Bonnet  and  Spallanzani.  In  the  history  of 
the  nineteenth  century  we  shall  have  to  consider  some  of 


CH.  XXX. 


SUMMARY.  281 


these  facts,  and  see  how  Cuvier,  Lamarck,  and  Darwin  have 
carried  out  the  study  of  physiology  to  great  results  in  our 
own  day.  But  we  have  still  more  to  include  under  Biology. 
After  learning  the  nature  of  living  beings,  we  must  have  some 
order  of  arrangement  by  which  we  can  distinguish  them. 
Here  we  come  to  the  work  of  Linn^us,  one  of  the  grandest 
men  of  the  eighteenth  century.  While  Buffon  was  popular- 
izing natural  history,  we  find  the  great  Swede  patiently 
working  out  all  the  minute  characters  and  general  features 
of  animals  and  plants,  and  reducing  the  whole  kingdom  of 
life  into  such  beautiful  order,  that  after  his  time  it  could  be 
studied  accurately  and  usefully  by  all  who  cared  to  take  time 
and  trouble. 

Thus,  even  without  mentioning  the  science  of  medicine, 
which  has  grown  far  beyond  our  power  of  following  it  up,  or 
the  wonderful  work  with  the  microscope,  which  had  increased 
rapidly  since  the  days  of  Grew  and  Malpighi,  biology  grew 
during  the  eighteenth  century  into  a  group  of  sciences, 
the  works  upon  which  would  fill  a  library,  and  each  branch 
of  which  requires  the  study  of  a  lifetime  to  master  it. 

Greology.— Side  by  side  with  biology  arose  about  this 
time  the  modest  and  almost  unnoticed  science  of  the  earthy 
then  generally  called  physical  geography,  but  now  known  as 
Geology.  This  was  a  small  seed  sown  in  the  eighteenth 
century,  to  grow  into  a  large  tree  only  in  our  time ;  yet  it 
was  a  great  step  when  Scilla  insisted  that  fossils  were  the 
remains  of  living  beings,  and  that  the  rocks  containing  them 
were  formed  gradually  under  lakes  or  seas.  And  when 
Werner  taught  men  to  study  the  earth's  crust,  and  Hutton 
forced  them  to  see  that  Nature  is,  and  has  always  been, 
building  up  our  present  world  out  of  the  ruins  of  the  past, 
the  foundations  were  laid  for  the  real  study  of  the  earth  and 


282  EIGHTEENTH  CENTURY.  pt.  hi. 

its  formation.  Meanwhile  William  Smith  toiled  over  Eng- 
land, mapping  out  the  position  of  each  rock  as  he  saw  it,  and 
thus  he  led  the  way  to  a  long  series  of  careful  observations, 
by  which  the  whole  geology  of  England  has  been  worked 
out. 

Chemistry. — But  the  science  which  before  all  stands 
forth  in  the  eighteenth  century  is  cheinisUj)  for  here  the 
discovery  of  the  different  gases  led  to  certainty  where  all  had 
been  guess-work  before,  showing  the  actual  chemical  changes 
which  are  taking  place  on  all  sides  in  the  world  around  us, 
and  teaching  men  to  weigh  and  test  invisible  substances,  and 
not  to  rest  satisfied  with  their  knowledge  of  any  substance  till 
they  had  traced  it  home  to  its  first  and  simplest  elements.  We 
need  not  recapitulate  here  the  different  discoveries  of  Scheele, 
Bergmann,  Black,  Cavendish,  Priestley,  and  Lavoisier.  You 
will  remember  how  they  all  helped  to  overthrow  the 
imaginary  theory  of  Phlogiston,  and  to  prove  that  combus- 
tion and  respiration  are  merely  chemical  changes  taking 
place  between  different  substances  and  the  oxygen  of  our 
atmosphere  ;  and  this  truth  is  the  starting-point  of  modern 
chemistry. 

Physics. — Of  Physics  I  have  told  you  but  little  in  this 
century,  but  the  two  points  we  have  considered  have  caused 
greater  changes  throughout  the  world  than  any  previous  dis- 
coveries. When  Black  proved  the  amount  of  heat  which  is 
lying  hid  in  water  and  in  steam,  and  when  Watt  applied 
it  to  the  steam-engine,  a  giant  power  was  bom  into  the 
world  which  has  worked  marvels.  Visit  any  of  the  little 
towns  all  over  England  and  see  the  machines  of  all  kinds 
moved  by  the  simple  power  of  steam  ;  then  go  to  the 
great  manufacturing  towns  and  see  the  huge  engines  doing 
the  work  of  thousands  of  horses,  with  no  other  help  than 


CH.  XXX.  SUMMARY.  283 

that  of  a  man  feeding  the  furnace  with  coals.  Look  at  any 
one  of  your  own  clothes,  at  the  ironwork  in  all  parts  of  your 
house,  from  the  rough  heavy  iron  of  fireplaces  and  fenders 
to  the  delicate  steel  spring  which  moves  the  hands  of  your 
watch ;  look  at  the  planks  on  your  floors,  and  the  carpets 
which  cover  them  !  All  these  have  been  woven,  and  forged, 
tempered,  sawn,  and  worked  by  steam  machinery.  Then 
think  of  the  way  in  which  people  are  carried  from  one  place 
to  another  of  the  world  ;  so  that  in  one  month  a  man  may 
be  in  India,  and  the  next  in  London  j  while  food,  clothing, 
and  goods  of  all  kinds  are  spread  over  different  countries  in 
a  few  weeks  whenever  they  are  wanted.  And  then  remem- 
ber that  all  this  has  sprung  out  of  the  latent  heat  of  steam, 
and  its  application  by  Watt  to  the  steam-engine. 

The  next  discovery  is  perhaps  even  more  wonderful. 
Franklin  tries  experiments  upon  the  peculiar  power  known 
by  the  name  of  electricity,  and  he  suspects  that  it  is  every- 
where and  in  everything.  He  proves  its  passage  from  one 
body  to  another,  and  finds  out  many  of  its  properties.  In 
spite  of  the  derision  of  his  friends,  he  seeks  to  bring  it 
down  from  the  sky,  and  succeeds  in  making  a  prisoner  of  the 
lightning  and  working  with  it  in  his  own  laboratory.  Galvani 
next  finds  this  wonderful  power  hidden  in  the  nerves  of  a 
frog ;  while  Volta  crowns  the  whole  by  showing  how  power- 
ful electricity  can  be  produced  by  two  metals  placed  in  a 
little  acid  and  water,  and  how  this  can  be  carried  along 
a  wire  of  any  length  which  touches  the  battery  at  both  its 
ends.  Here  lies  hid  the  germ  of  the  electric  telegraph  \  but 
the  grand  secret  of  carrying  messages  from  one  end  of  the 
world  to  another  in  a  few  moments  was  not  to  come  yet. 
That  remained  for  the  nineteenth  century  to  accomplish. 

Astronomy — Lastly  we  come  to  astronomy,  and  to  some 


284  EIGHTEENTH  CENTURY.  pt.  hi. 

of  the  most  tremendous  problems  in  the  working  of  our 
universe.  Here  we  find  Lagrange  proving  that  the  system 
of  our  sun  and  planets  is  self- regulating,  so  that  in  spite  of 
all  its  infinite  changes,  there  is  no  real  irregularity  or  change- 
ableness  in  its  machinery,  but  all  moves  in  one  perfect  and 
constant  round.  Laplace  shows  the  reason  of  those  irregu- 
larities which  seemed  to  contradict  Newton's  law  of  gravita- 
tion, and  proves  that  they  are  all  explained  by  that  law, 
thus  completing  the  work  of  the  great  astronomer.  Then 
Herschel  takes  up  the  story,  and  after  discovering  a  new 
planet,  he  studies  the  cloudy  nebulae,  and  points  out  the 
probable  formations  of  new  suns  going  on  now  in  far-distant 
regions;  he  pictures  our  own  sun  rushing  through  space  at 
the  rate  of  150,000,000  miles  a  year,  carrying  with  it  our 
earth  and  all  the  other  planets  ;  and  above  all  he  traces 
the  law  of  gravitation  into  the  distant  star- world,  and  shows 
it  there  holding  suns  together  and  causing  them  to  revolve 
round  each  other.  And  so,  out  into  space  as  far  as  the 
mind  can  reach,  we  find  everlasting  order  reigning  through 
out  the  visible  universe. 


List  of  Works  consulted. — Herschel's  'Astronomy;'  Arago,  *Vie 
et  travaux  de  Herschel,'  1S43  ;  Proctor's  'Essays  on  Astronomy,' 
'  The  Universe, '  'Other  Worlds  than  Ours' j  Grant's  'History  of 
Physical  Astronomy  ; '  Arago,  '  Eloge  of  Laplace ; '  Airy's  '  Astro- 
nomy ; '  '  Encyclopsedia  Britannica '  —  '  Astronomy  ;  '  '  Orbs  of 
Heaven,'  Mitchell. 


SCIENCE    OF    THE 
NINETEENTH    CENTURY 


Some  of  the  Chief  Men  of  Science  of  the  i<^tk  Century 
who  are  mentioned  in  the  following  pages. 


Piazzi 

Olbers     . 

Encke 

Gauss 

Sir  J.  Herschel 

Airy 

Adams    . 

Leverrier 

Galle       . 

Schwabe 

Young     . 
Malus 
Fresnel   . 
Arago 
Seebeck  . 
Oersted  . 
Ampere  . 
Brewster 
Sabine     . 
Fraunhofer 
Wheatstone 
Bunsen    . 
Kirchhoff 


A.D. 
I  746- 1 826 

I 758-1 840 

I79I-I865 

I777-I855 
I792-I87I 

1 80 1,  living 
1818,  living 
181 T,  living 
18 12,  living 
1788-1875 

1773-1829 
1775-1812 
I 788-1 82 7 
1786-1853 
1770-1831 
1777-1851 
1779-1864 
I 784-1 868 
1 788,  living 
I 787-1 826 
1802-1875 
181 1,  living 
1824,  living 


Huggins 

A.D. 

1824,  living 

Miller      . 

1817-1870 

Wollaston 

1766-1828 

Biot 

.     I 774-1862 

Berzelius 

1779-1848 

Dalton     . 

.     1767-1844 

Davy       .\ 

.     1778-1829 

Faraday'. 

1791-1867 

Liebig     . 

.     I 803- I 873 

Humboldt 

.     1767-1835 

Buckland 

.     1 784-1856 

Lyell       . 

.     1797-1875 

Agassiz   . 

.     1807^1873 

Lamarck 

.     I 744-1829 

Goethe    . 

I 749-1833 

Cuvier     . 

I 769-1 832 

G.  St.  Hilaire 

1 772-1844 

Von  Baer 

1792,  living 

Boucher  de  Perthes 

I 788-1868 

Wallace  . 

1822,  living 

Darwin   . 

1809,  living 

CH.  XXXI.  ASTRONOMY.  287 


CHAPTER  XXXI. 

SCIENCE   OF   THE   NINETEENTH    CENTURY. 

Difficulties  of  Contemporary  History  —  Discovery  of  Asteroids  or 
Minor  Planets  between  Mars  and  Jupiter — Dr.  Olbers  suggests  they 
may  be  fragments  of  a  larger  Planet — Encke's  Comet,  and  the  cor- 
rection of  the  size  of  Jupiter  and  Mercury — Biela's  Comet  noticed 
in  1826 — It  divides  into  two  Comets  in  1845 — Irregular  movements 
of  Uranus — Adams  and  Leverrier  calculate  the  position  of  an  un- 
known Planet — Neptune  found  by  these  calculations  in  1846 — A 
Survey  of  the  whole  Heavens  made  by  Sir  John  Herschel— His 
work  in  Astronomy — Comets  and  Meteor- systems. 

We  have  now  arrived  fairly  at  the  beginning  of  our  own 
century,  and  shall  have  to  speak  of  events  which  happened 
as  it  were  but  yesterday,  and  of  men  whom  our  grandfathers, 
or  even  perhaps  our  fathers,  have  seen  and  known.  How 
are  we  to  find  our  way  through  the  mass  of  discoveries 
which  have  been  made  in  every  science  during  the  last 
seventy  years,  or  to  make  our  choice  among  the  number  of 
famous  men  whose  names  we  meet  with  every  day  ?  We 
must  begin  at  once  by  recognising  that  it  is  impossible  to 
mention  all,  even  of  the  leading  points,  of  the  science  of  our 
time,  and  then  we  may  try  to  learn  a  few  of  them,  if  we  do 
so  with  a  clear  understanding  that  we  are  leaving  important 
gaps  unfilled. 

There  are  two  special  difficulties  which  we  must  en- 
counter in  the  history  of  this  century;  first,  we  cannot 
avoid  mentioning  the  work  of  some  living  men,  while  at  the 


288  NINETEENTH  CENTURY.  pt.  in. 

same  time  we  omit  others  who  are  equally  eminent ;  and 
secondly,  we  must  speak  of  many  subjects  which  are  still,  as 
it  were,  on  their  trial,  and  which  will  not  be  finally  settled 
till  they  can  be  judged  dispassionately  by  future  generations. 
I  have  tried,  however,  to  follow  as  far  as  possible  the  plan  I 
adopted  in  the  earlier  centuries,  of  mentioning  only  a  few 
great  men  whose  work  you  can  understand  and  follow;  and 
stating  on  doubtful  subjects  what  is  the  opinion  of  those  who 
are  best  able  to  judge  from  the  evidence.  Therefore  you 
must  constantly  bear  in  mind  that  this  last  portion  of  the 
book  cannot  be  said  to  contain  a  history  of  the  science  of 
the  nineteenth  century,  but  only  an  account  of  a  few  of  the 
leading  discoveries  and  theories  of  our  times  and  of  the  men 
who  made  them. 

Advance  in  Astronomy. — The  science  of  Astronomy,  in 
particular,  has  spread  far  beyond  our  power  to  follow  it. 
We  have  seen  that  astronomers  up  to  the  end  of  the 
eighteenth  century  were  always  striving  to  work  out  the  laws 
which  govern  the  movements  of  the  heavenly  bodies.  The 
key  to  this  problem  was  found  by  Newton,  and  the  work  was 
completed  when  Laplace  and  Lagrange  showed  that  even 
those  planets  which  seem  to  have  the  most  irregular  orbits 
are  really  governed  by  the  force  of  gravitation.  From  that 
time  astronomy  became  really  an  exact  science,  and  men  had 
only  to  make  their  calculations  with  perfect  accuracy  in 
order  to  be  able  to  foretell  what  was  going  to  happen  ;  or  if 
they  failed,  then  they  knew  there  must  be  some  other  un- 
known heavenly  body  (such  as  Neptune,  p.  294)  causing  the 
irregularity.  Therefore,  the  science  of  astronomy  in  our 
century  has  been  chiefly  occupied  in  discovering  new  planets, 
stars,  and  star-clusters ;  at  every  step  giving  us  new  proof 
that  gravitation  rules  throughout  the  visible  universe.     And 


CH.  XXXI.       ASTEROIDS  OR  MINOR  PLANETS.  289 

side  by  side  with  this  has  grown  up  a  new  study,  namely 
that  of  the  nature  of  the  sun,  planets,  stars,  comets,  meteors, 
&c.,  telling  us  what  they  are  like  in  themselves,  whether  they 
have  an  atmosphere  like  our  own,  and  of  what  materials 
they  are  made.  This  study  has  been  carried  on  partly  by 
powerful  telescopes,  but  chiefly  by  the  wonderful  method 
called  spectru77i  analysis,  of  which  we  shall  speak  presently. 
Meanwhile  we  must  first  begin  by  naming  a  few  new  bodies 
lately  observed  in  the  heavens. 

Discovery  of  the  Asteroids  and  Minor  Planets  between 
Mars  and  Jupiter,  1801-1807.— Not  long  after  the  dis- 
covery of  Uranus,  a  well-known  astronomer  named  Bode 
pointed  out  that  the  distances  of  the  planets  from  the  sun 
seemed  to  follow  a  remarkable  arithmetical  law.  The  only 
exception  to  this  law  was  between  Jupiter  and  Mars ;  and 
here  the  gap  was  t\vice  as  large  as  it  ought  to  be  according 
to  the  calculation.  Therefore  astronomers  suspected  that 
there  must  be  a  planet  between  these  two  which  had  not 
yet  been  seen ;  and  in  the  year  1 800,  at  a  meeting  at  Lilien- 
thal,  in  Saxony,  they  agreed  to  search  diligently  for  this  sup- 
posed missing  body. 

Signor  Piazzi,  the  Astronomer  of  the  Observatory  at 
Palermo,  in  Sicily,  was  one  of  these  planet-searchers,  and  on 
the  first  night  of  the  year  1801  he  caught  sight  of  a  small 
star  in  the  constellation  Taurus,  which  had  not  yet  been 
noticed  in  any  catalogue.  The  next  night  he  looked  for  it 
again,  and  found  that  it  had  moved  its  position.  He  did 
this  for  twelve  nights,  and  the  movement  seemed  to  show 
that  it  was  the  planet  he  was  seeking.  Just  at  this  point, 
however,  he  was  taken  ill,  and  although  he  had  told  other 
astronomers  of  what  he  had  seen,  no  one  could  find  the 
planet  again.  Months  passed,  and  people  began  to  doubt 
14 


290  NINETEENTH  CENTURY.  pt.  iii. 

whether  he  had  not  made  a  mistake ;  but  at  last  a  young 
German  astronomer  named  Gauss  set  to  work  to  calculate, 
from  the  facts  which  Piazzi  had  given,  whereabouts  in  the 
heavens  the  planet  ought  then  to  be,  and  turning  his  tele- 
scope to  the  point,  there  he  found  it !  This  planet  was 
called  Ceres;  it  was  very  small  compared  to  the  other 
planets,  but  the  astronomers  were  satisfied  at  having  filled 
up  the  supposed  gap. 

Before  two  years  had  passed  away,  however,  in  the  year 
1802,  another  astronomer,  Dr.  Olbers,  of  Bremen,  suddenly 
announced  that  he  had  found  another  little  planet  near 
Ceres,  which  he  called  Pallas,  and  in  1804  a  third  was  found 
by  another  astronomer  named  Harding,  who  called  it  Juno. 
It  seemed  very  strange  that  so  many  bodies  should  be 
moving  round  the  sun  at  nearly  the  same  distance  from 
it,  and  Dr.  Olbers  suggested  that  they  might  perhaps  be 
parts  of  one  large  planet  which  had  broken  up  into  fragments. 
If  this  was  so  he  expected  to  find  more,  and  truly  enough  in 
1807  a  fourth  was  discovered,  which  he  called  Vesta.  In 
1845  and  1847  two  more  were  added  to  the  number. 
Since  then  some  have  been  found  every  year,  till  now  no 
less  than  153  of  these  small  planets,  or  asteroids  as  they 
are  called,  are  known  to  be  moving  round  the  sun  be- 
tween Mars  and  Jupiter.  Pallas,  the  largest  of  these,  only 
measures  about  600  miles  across,  and  when  it  comes  nearest 
to  the  earth  does  not  look  larger  than  a  star  of  the  eighth 
magnitude.  Whether  they  are  really  fragments  of  a  planet  is 
not  proved,  and  we  have  still  a  great  deal  to  learn  about  them. 

Encke's  Comet,  1819. — The  next  bodies  of  interest  which 
were  discovered  were  two  returning  comets,  each  of  them 
remarkable  for  different  reasons.  The  first  of  these  was 
observed  in  181 9,  through  the  telescope  at  Marseilles,  by  a 
Freiicliman  named  Pons.     It  was  very  small,  and  is  mainly 


CH.  XXXI.  RETURNING  COMETS,  291 

of  importance  because  after  Professor  Encke,  of  Berlin,  had 
calculated  that  it  returned  regularly  every  three  years  and  a 
quarter,  he  found  that  it  arrived  two  hours  and  a  quarter 
earlier  each  time.  "Why  it  should  come  earlier  is  a  question 
which  is  still  very  perplexing  to  astronomers,  though  several 
explanations  have  been  suggested.  In  order  to  find  out 
how  fast  this  comet  moved,  Encke  was  obliged  to  calculate 
very  accurately  how  much  the  different  planets  attract  it ; 
and  this  led  him  to  discover  that  Jupiter  is  larger  than  the 
earlier  astronomers  had  supposed,  while  Mercury  is  much 
smaller. 

Biela's  Comet,  1826. —  In  1826  another  remarkable 
comet  was  observed  by  an  Austrian  officer  named  Biela, 
and  on  that  account  called  *  Biela's  comet'  M.  Clausen,  a 
German  astronomer,  computed  that  it  revolved  in  an  elliptic 
orbit  in  a  period  of  six  years  and  eight  months,  and  it  was 
then  shown  to  be  the  same  comet  which  had  been  observed 
in  1772, 1805,  and  1818.  This  comet  has  had  a  very  curious 
history.  In  the  year  1832  great  alarm  was  excited  because 
the  astronomers  calculated  that  it  would  cross  the  orbit  of 
our  earth  on  October  29.  People  who  did  not  understand 
the  question  thought  this  meant  that  it  would  run  into  us 
and  perhaps  destroy  our  earth ;  and  many  even  sold  their 
houses  and  land  because  they  thought  the  end  of  the  world 
was  at  hand.  The  people  in  Paris  especially  were  so 
frightened  about  it  that  the  Academy  of  Sciences  were 
obliged  to  ask  Arago,  the  French  astronomer,  to  quiet  their 
fears,  and  he  wrote  a  popular  essay  showing  that  though  the 
comet  crossed  the  path  of  our  earth,  yet  on  that  day  we 
should  be  fifty-five  millions  of  miles  away  from  the  spot. 

But   it   was   in    1845    ^^^   Biela's  comet  proved  most 
interesting.     On  November  26  in  that  year  it  came  at  the 


292  NINETEENTH  CENTURY.  pt.  hi. 

time  it  was  expected,  and  was  seen  each  night  afterwards  as 
usual  till  January  12.  On  that  night,  however,  when 
Lieutenant  Maury  looked  at  it  from  the  observatory  at 
Washington,  in  the  United  States,  he  saw,  not  one  comet,  but 
two  distinct  and  separate  comets  moving  along  together.  This 
seemed  so  strange  that  it  would  scarcely  have  been  believed 
if  several  astronomers  had  not  watched  the  comet  for 
more  than  a  month,  and  satisfied  themselves  that  it  had 
really  split  up  into  two  parts,  each  part  being  a  perfect 
comet,  with  a  bright  head  and  a  glowing  tail !  These  two 
comets  returned  in  1852,  still  keeping  each  other  company 
at  the  same  distance  apart  as  in  1846,  but  since  then  they 
have  never  been  seen  again.  Many  other  comets  have  been 
discovered  besides  these,  and  we  know  that  many  thousands 
or  even  millions  must  be  wandering  through  space,  but  of 
these  we  cannot  speak  here. 

Adams  and  Leverrier  determine  the  Position  of  an 
Unknown  Planet  by  its  Influence  on  the  Orbit  of  Uranus, 
1843-1848. — The  next  discovery  which  we  must  consider  is 
one  of  the  most  remarkable  in  the  history  of  astronomy, 
because  it  was  not  made  with  the  telescope  but  was  worked 
out  independently  by  two  men  entirely  by  means  of  Newton's 
theory  of  gravitation.  You  will  remember  that  in  1781  Sir 
William  Herschel  discovered  the  planet  Uranus  moving  out- 
side all  the  other  planets  (see  p.  272).  Now  many  astrono- 
mers had  noticed  this  body  in  earlier  ages,  and  supposing  it 
to  be  a  star,  had  marked  its  position  from  time  to  time  in  the 
heavens,  and  from  these  observations  it  was  now  possible 
to  calculate  its  path  round  the  sun.  When  this  was  done 
it  was  found,  however,  that  the  planet  did  not  move  as 
it  ought  to  do  according  to  the  theory  of  gravitation.  The 
pull  of  the  sun  and  the  known  planets  did  not  account  for 


CH.  XXXI.  DISCOVERY  OF  NEPTUNE.  293 

its  orbit,  for  it  roamed  farther  out  into  space  than  it  should 
do  if  they  were  the  only  bodies  which  attracted  it.  Either, 
therefore,  the  early  astronomers  had  marked  the  position  of 
the  planet  wrongly,  or  some  unknown  and  unseen  body 
m-ust  be  pulling  it  out  of  its  course.  This  last  seemed  the 
most  likely  explanation,  but  no  such  planet  could  be  seen, 
and  the  problem  remained  unsolved. 

It  was  at  this  point  that  a  young  student  of  St.  John's 
College,  Cambridge,  named  John  Couch  Adams,  then  only 
twenty-three  years  of  age,  made  a  memorandum  in  his  note- 
book to  work  out  the  movements  of  Uranus,  and  see  if  by 
this  means  he  could  discover  whether  there  was  another 
planet  farther  away  from  the  sun.  As  soon  as  he  had  taken 
his  degree  as  Senior  Wrangler  in  1843,  ^^  set  to  work  to 
carry  out  his  intention,  and  two  years  afterwards  he  sent  a 
paper  to  Mr.  Airy,  the  Astronomer-Royal  at  Greenwich, 
stating  in  what  part  of  the  heavens  astronomers  ought  to 
look  for  the  unknown  planet  which  would  explain  the 
capricious  movements  of  Uranus. 

It  is  not  easy  for  any  but  mathematicians  to  understand 
what  a  wonderful  thing  it  was  to  calculate  accurately,  in  this 
way,  where  a  planet  would  be  found  which  had  never  been 
seen.  When  Pallas  was  discovered  between  Mars  and  Jupi- 
ter, Piazzi  saw  it  through  the  telescope  for  some  days,  and 
it  was  only  found  again  by  following  out  the  movement 
which  he  had  recorded.  But  in  Adams's  case  nothing  had 
ever  been  seen,  and  the  only  reason  for  suspecting  anything 
to  be  there,  was  that  astronomers  could  not  make  their  very 
difficult  calculations  of  the  attraction  of  the  different  planets 
come  out  right.  Adams,  therefore,  had  first  to  calculate  all 
the  attractions  of  the  sun  and  the  planets,  in  their  different 
positions,  and  then  to  find  out  how  they  would  affect  Uranus 


294  NINETEENTH  CENTURY.  pt.  in. 

in  his  path  ;  and  wherever  the  planet  did  not  follow  their 
pulling  he  had  to  calculate  where  another  body  must  be  to 
draw  it  away  from  them.  This  he  accomplished,  and  it  is 
very  remarkable  that  the  great  living  French .  astronomer 
named  Leverrier  also  worked  out  the  same  problem,  without 
having  heard  that  Adams  had  done  it 

In  the  year  1839  Leverrier  had  begun  a  long  series  of 
calculations  (which  were  only  completed  last  year,  1874),  to 
find  out  the  varying  attractions,  and  by  that  means  the  size 
and  weight,  of  the  different  planets,  and  while  he  was  at 
work  at  this  he  became  convinced  that  there  must  be  some 
unseen  body  pulling  at  Uranus.  Now  it  so  happened  that 
just  at  the  time  when  Adams  and  Leverrier  began  to  feel 
after  this  supposed  planet,  Uranus  had  lately  been  very  much 
disturbed,  and  so  they  knew  that  the  disturbing  cause  must 
have  approached  near  to  him,  and  this  showed  them  in 
which  part  of  the  heavens  the  attracting  planet  ought  to  be. 

Leverrier  published  his  calculations  in  the  Journal  of 
the  Academie  des  Sciences  at  Paris  for  June  1846,  and  when 
the  Astronomer- Royal  read  the  paper  he  was  astonished  to 
find  that  the  French  astronomer  had  fixed  the  place  of  the 
unknown  planet  within  one  degree  of  the  spot  which  Adams 
had  named.  This  led  him  to  read  Adams's  paper  again 
more  carefully,  and  to  put  the  two  astronomers  into  com- 
munication with  each  other ;  and  the  consequence  was  that 
Leverrier  wrote  another  paper  in  August  1846,  stating  still 
more  accurately  where  the  planet  ought  to  be  found.  This 
paper  he  sent  to  his  friend  M.  Galle,  of  the  Berlin  Obser- 
vatory, on  September  23,  1846,  asking  him  to  look  for 
the  planet  in  that  part  of  the  sky  which  he  pointed  out.  M. 
Galle  did  so,  and  on  that  sa??ie  night,  by  foUoming  the  instruc- 
tions of  the  two  astronomers^  he  found  the  unknown  planet. 


CH.  XXXI.  SIR  JOHN  HERSCHEL.  295 

So  true  is  the  law  of  gravitation  that  two  men  sitting  at 
home  in  their  studies  were  enabled,  from  slight  irregularities 
in  the  motion  of  Uranus  to  predict  the  existence  and  place 
of  a  disturbing  body,  rolling  on  through  space  !  This  new 
planet  is  called  Neptune,  and  is  a  little  larger  than  Uranus; 
it  has  certainly  one  moon,  discovered  by  M.  Lassell,  and 
Herr  Struve  thinks  he  has  seen  a  second. 

Sir  John  Herschel's  work  in  Astronomy. — While  these 
different  discoveries  were  being  made  in  the  observatories  of 
Europe,  Sir  John  Herschel  was  carrying  on  the  work  his 
father  had  begun  of  gauging  or  measuring  the  brilliancy  of 
the  stars.  Born  at  Slough,  close  to  his  father's  observatory^, 
in  1792,  the  young  John  Herschel  spent  his  early  life  with 
his  father  and  aunt,  and  saw  them  always  busy  night  and 
day  studying  the  heavens.  In  18 13  he  was  Senior  Wrangler 
at  Cambridge,  and  after  that  he  turned  his  attention  to 
double  stars,  and  in  1828  completed  a  list  of  no  less  than 
2,000  of  these  wonderful  double  and  sometimes  treble  suns 
which  revolve  round  each  other.  When  he  had  completed 
the  survey  of  the  whole  of  our  northern  skies,  he  went  in 
1833  to  the  Cape  of  Good  Hope,  where  an  observatory 
had  been  built  in  1820,  and  there  he  spent  four  years 
gauging  the  stars  of  the  southern  hemisphere  and  classing 
them  according  to  their  brilliancy,  as  his  father  had  classed 
those  of  the  northern  hemisphere.  He  was  thus  the  first 
astronomer  who  swept  his  telescope  over  the  whole  of  the 
heavens  which  are  visible  from  our  planet,  and  who  saw 
with  his  own  eyes  every  star,  planet,  and  nebula  then 
visible  in  the  sky.  Among  the  remarkable  appearances 
which  he  examined  were  those  cloudy  masses  of  light  called 
the  Magellanic  Clouds^  which  are  the  Milky  Way  of  the 
southern  hemisphere,  and  he  found  them  to  be  made  up  of 


296    .  NINETEENTH  CENTURY.  pt.  hi. 

Stars,  star-clusters,  and  nebulas,  mingled  together  in  wonder- 
ful complexity. 

When  he  returned  to  England  in  1838,  you  can  imagine 
what  a  wonderful  picture  he  must  have  had  in  his  mind  of 
the  whole  universe  as  far  as  we  can  see  it.  It  was  then  that 
he  wrote  his  famous  '  Outlines  of  Astronomy,'  which  was  a 
new  edition  of  a  little  book  he  had  written  years  before.  In 
this  great  work  Sir  John  Herschel  first  taught  ordinary 
people  what  a  grand  science  astronomy  is.  Before  his  time 
the  different  discoveries  and  theories  had  been  scattered 
about  in  various  scientific  papers,  too  difficult  and  too 
tedious  for  the  public  to  read.  But  Sir  John  wrote  simply 
and  plainly  about  the  great  truths  which  had  been  worked 
out  from  the  days  when  Aristarchus  first  asserted  that  the 
earth  moved  round  the  sun  to  the  time  when  Sir  William 
Herschel  pictured  our  whole  solar  system  travelling  onwards 
through  endless  space ;  and  through  his  book  many  who 
would  never  otherwise  have  studied  the  science  learnt  to 
know  something  of  the  wonders  of  the  heavens  and  the 
lessons  they  teach.  Sir  John  was  a  true  lover  of  the  works 
of  nature,  and  he  taught  all  his  readers  to  love  them  too, 
and  to  feel  a  true  reverence  for  the  Infinite  Mind  of  the 
Creator  of  them  all.  He  died  in  1871,  and  was  buried  in 
Westminster  Abbey,  but  never  will  those  who  knew  him 
forget  the  beautiful  truth-loving  spirit  which  breathed  in 
every  word  he  wrote  or  spoke. 

Sir  John  Herschel  is  the  last  of  our  great  astronomers 
who  is  no  longer  living,  and  here  we  should  close  the  history 
of  physical  astronomy,  if  it  were  not  that  a  wonderful  disco- 
very has  been  made  within  the  last  ten  years  which  must  at 
least  be  mentioned. 
Discovery  of  the  Paths  along  which  Meteors  travel, 


CH.  XXXI.  METEORS.  297 

and  the  Agreement  of  two  of  these  with  the  Orbits  of  Re- 
turning Comets,  1862. — Everyone  has  heard  of  falling  or 
shooting-stars,  and  most  people  have  probably  seen  one  or 
more  of  these  bright  meteors  rush  across  the  sky  on  a  calm 
summer  evening,  and  then  vanish  as  suddenly  as  it  appeared. 
The  rude  Lithuanian  peasants  have  a  touching  legend  about 
these  falling  stars.  'To  every  new-born  child,'  they  say, 
*  there  is  attached  an  invisible  thread,  and  this  thread  ends 
in  a  star  ;  when  that  child  dies  the  thread  breaks,  and 
the  light  of  the  star  is  quenched  as  it  falls  to  the  earth.' 
Science  has  taught  us  a  different,  but  a  not  less  wonderful 
history.  It  is  now  known  that  these  meteors  are  solid 
stones,  'pocket  planets'  as  Humboldt  called  them,  which 
travel  round  the  sun  in  the  opposite  direction  to  that  in 
which  we  are  going,  "WTien  we  meet  them  they  rush  through 
our  atmosphere  so  fast  that  they  become  heated,  and  give  out 
light  for  a  short  time  till  they  are  burst  into  fine  dust  and 
vanish.  When  they  are  too  large  to  be  consumed  before 
they  reach  the  earth,  they  fall,  often  with  great  violence,  and 
are  split  into  countless  fragments.  A  large  collection  of 
these  meteoric  stones  is  to  be  seen  in  the  British  Museum, 
some  weighing  hundreds  of  pounds,  others  only  a  few  grains. 
They  have  been  analysed,  and  are  found  to  be  composed 
chiefly  of  iron,  tin,  sulphur,  olivine,  and  oxygen. 

Before  the  present  century  all  that  was  known  about  these 
bodies  was  very  vague  and  unsatisfactory.  From  time  to  time 
accounts  of  stone-falls  came  from  different  parts  of  the  world, 
but  they  were  not  much  attended  to,  and  people  found  it 
difficult  to  believe  that  stones  and  mineral  masses  actually 
fell  from  the  sky  on  to  the  earth.  But  in  1803  a  fiery  globe 
was  seen  to  rush  over  the  town  of  Aigle,  in  Normandy,  and  a 
stony  mass  was  dashed  to  the  ground  and  shattered  into 


298  NINETEENTH  CENTURY.  pt.  hi. 

thousands  of  fragments,  some  of  which  weighed  as  much  as 
1 7  J  lbs.  This  created  so  much  astonishment  that  the  French 
Government  sent  M.  Biot,  a  celebrated  French  chemist,  to  ex- 
amine into  the  matter,  and  he  reported  that  there  could  be  no 
doubt  that  a  shower  of  hot  stones  had  fallen  upon  the  earth. 

From  this  time  more  interest  was  taken  in  meteors  and 
meteoric  stones.  People  had  remarked  for  a  long  time  that 
shooting-stars  were  more  abundant  from  the  9th  to  the  nth 
of  August  than  at  other  times,  and  more  lately  it  was  also 
noticed  that  a  shower  of  the  same  kind  happens  about  the 
T3th  of  November.  Astronomers  began,  therefore,  to  think 
that  these  meteors  must  move  in  regular  orbits,  crossing 
the  orbit  of  our  earth  in  certain  places,  so  that  we  pass 
through  them.  There  were  also  reasons  for  thinking  that 
the  November  meteors  travelled  in  an  enormous  ellipse, 
passing  at  one  end  even  outside  the  planet  Uranus. 

It  was  not,  however,  till  thirteen  years  ago  that  anything 
was  really  known.  In  the  year  1862  an  Italian  astronomer 
named  Schiaparelli  made  a  very  remarkable  suggestion.  He 
noticed  that  a  comet  which  was  seen  in  that  year  crossed  the 
earth's  path  just  at  the  point  where  we  are  always  in  the 
middle  of  the  meteor- shower  on  August  10,  and  it  occurred 
to  him  whether  it  might  not  be  possible  that  the  August 
meteors  were  travelling  in  the  same  orbit  as  the  comet.  His 
guess  turned  out  perfectly  right,  and  by  a  calculation  which 
we  cannot  follow  here  he  proved  that  the  comet  and  the  August 
meteors  travel  along ;precisely  the  same  path  in  the  shape  of  a 
long  ellipse  passing  at  one  end  outside  the  planet  Neptune, 
the  most  distant  of  the  known  planets.  This  was  the  first 
time  that  the  orbit  of  any  set  of  meteors  had  been  traced 
out. 

The  next  was  that  of  the  November  meteors,  which  was 


CH.  XXXI.  METEOR-SHOWERS.  299 

determined  by  Adams,  and  also  independently  by  Leverrier. 
It  had  been  shown  by  searching  out  all  the  past  accounts  of 
November  showers  that  in  times  gone  by,  the  earth  passed 
through  these  meteors  a  little  earlier  in  the  year  than  she 
does  now,  and  this  could  not  be  accounted  for  by  any 
irregularity  in  the  movement  of  the  earth.  It  looked  there- 
fore as  if  the  orbit  of  the  November  meteors  must  be  slowly 
shifting,  just  as  the  orbits  of  the  planets  do,  within  certain 
limits.  It  was  upon  this  shifting  that  Adams  founded  his 
calculations,  and  he  worked  out  the  meteor  path  with  great 
accuracy,  showing  that  those  astronomers  had  been  right 
who  thought  it  extended  beyond  Uranus.  This  time  the 
problem  was  solved  by  pure  astronomical  reasoning  and  not 
by  a  happy  guess.  But  perhaps  the  most  remarkable  part 
of  the  story  is  that  in  1866,  long  after  Adams  had  deter- 
mined the  orbit,  a  new  comet  was  seen  which  was  found  to 
move  exactly  along  the  path  of  the  November  meteors,  in  the 
same  way  that  the  comet  of  1 8 1 2  agrees  with  those  which 
fall  in  August. 

Although  these  two  meteor-showers  are  the  most  impor- 
tant, they  are  by  no  means  the  only  ones  crossed  by  our  earth. 
Any  clear  night,  if  you  watch  carefully,  you  may  see  (according 
to  the  astronomer  Proctor)  about  six  shooting- stars  in  one 
hour;  and  Professor  Newton,  of  America,  has  calculated  that 
7,500,000  meteors  large  enough  to  be  seen  without  a  telescope 
pass  through  our  atmosphere  in  one  single  day  and  night. 
At  least  a  hundred  sets  of  meteors,  or  meteor-systems  as  they 
are  called,  are  known  to  astronomers,  and  each  one  of  these 
is  composed  of  millions  of  bodies;  and  you  must  bear  in 
mind  that  these  systems  do  not  move  round  us,  but  round 
the  sun,  so  that  it  is  only  because  we  happen  to  cross  their 
path  that  we  know  anything  of  them.     It  would  be  idle  to 


300  NINETEENTH  CENTURY.  pt.  hi. 

suppose  that  these  hundred  meteor- systems  which  we  come 
across  are  the  only  ones  existing.  On  the  contrary,  we 
have  every  reason  to  think  that  they  are  only  a  few  out  of 
thousands  of  meteor-systems  which  we  never  meet,  and 
which  must  grow  more  numerous  the  nearer  they  approach 
the  sun. 

And  so  we  arrive  a,t  the  wonderful  thought  that  the 
whole  of  our  solar  system  is  swarming  with  meteors  rushing 
along  with  immense  speed  !  What  their  use  is  we  do  not 
know.  Some  astronomers  imagine  that  the  heat  of  the  sun  is 
kept  up  by  these  meteoric  stones  falling  in  countless  myriads 
on  his  face,  but  this  is  disputed  by  others ;  and  for  the  pre- 
sent it  is  enough  if  we  can  picture  to  ourselves  these  rings 
of  meteors  whirling  round  and  round  in  space,  and  flash- 
ing into  light  as  they  rush  through  our  atmosphere  whenever 
we  happen  to  cross  their  path. 

I  have  chosen  out  these  new  facts  about  meteors  be- 
cause, of  all  modern  discoveries,  they  give  the  best  idea  of 
the  wide  fields  of  knowledge  which  are  opening  out  before 
us.  Within  the  last  fifty  years  a  number  of  most  interesting 
observations  have  been  made  about  the  nature  of  the  sun 
itself;  but  they  would  require  long  explanations,  and  being 
all  the  work  of  living  men  they  scarcely  belong  to  our 
history. 

In  the  chapter  on  Spectruni  Analysis  we  shall  learn  some- 
thing of  the  atmosphere  of  the  sun  and  stars,  and  in  the 
chapter  on  Magnetism  something  of  the  spots  on  the  sun 
and  their  effects  on  our  earth.  But  for  the  history  of  the 
discovery  of  the  photosphere,  corona,  red  prominences,  and 
other  wonderful  appearances  upon  the  face  of  the  sun,  you 
must  read  special  works  on  the  subject. 


CH.  XXXI.  ASl^RONOMICAL    WORKS.  301 

Chief  Works  consulted. — Airy's  'Report  on  Astronomy,'  British 
Association,  1833  ;  J.  D.  Forbes's  *  Progress  of  Mathematical  and 
Physical  Science ' — Sixth  Dissertation  ;  '  Encyclopaedia  Britannica,' 
new  edition  ;  Guillemin,  *  The  Heavens  ;  '  Herschel's  'Astronomy  ;' 
Grant's  '  Physical  Astronomy;'  'Reports  of  the  Astronomical  So- 
ciety;' '  The  Orbs  of  Heaven,'  Mitchell ;  Proctor,  '  On  Shooting- 
Stars  and  Meteors.' 


302  NINETEENTH  CENTURY.  pt.  hi. 


CHAPTER  XXXII. 

SCIENCE   OF   THE   NINETEENTH   CENTURY   (CONTINUED). 

Discoveries  concerning  Light  made  in  the  Nineteenth  Century — Birth 
and  History  of  Dr.  Young — He  explains  the  Interference  of  Light 
— Cause  of  Prismatic  Colours  in  a  Shadow — And  in  a  Soap-bubble 
— Malus  discovers  the  Polarization  of  Light  caused  by  Reflection — 
Birth  and  History  of  Fresnel — Polarization  of  Light  explained  by 
Young  and  Fresnel — Complex  Vibrations  of  a  Ray  of  Light — How 
these  Waves  are  reduced  to  two  separate  Planes  in  passing  through 
Iceland  Spar — Sir  David  Brewster  and  M.  Biot  explain  the  colours 
produced  by  Polarization. 

We  must  now  go  back  to  the  history  of  Light,  which  we  left,  as 
you  will  remember,  at  the  end  of  the  seventeenth  century,  at 
the  point  which  Newton  and  Huyghens  had  reached.  During 
the  whole  of  the  eighteenth  century  very  little  was  learnt  about 
this  science,  and  it  remained  for  the  men  of  our  own  time  to 
make  the  next  step  and  to  discover  the  grand  laws  of  light 
which  we  must  now  consider.  It  will  be  best  to  divide  our 
subject  into  two  parts — ist.  The  discoveries  which  have  led 
to  a  true  Theory  of  Light.  These  are  very  difficult  to  under- 
stand, and  you  must  not  expect  to  gain  more  than  a  slight 
notion  of  them ;  2nd.  The  new  facts  lately  discovered  about 
the  Chemistry  of  Lights  and  called  Spectrum  Analysis,  and 
of  these  I  hope  you  may  understand  enough  to  fill  you  with 
delight  at  the  beautiful  histories  they  reveal. 

Discovery  of  the  Interference  of  Light  by  Young,  1801. — 
You  will  remember  that  Newton  and  Huyghens  had  proposed 


CH.  XXXII.  DR.  THOMAS   YOUNG,  303 

two  different  theories  of  light  (see  page  174).  Newton's, 
called  the  Corpuscular  or  Emission  Theory,  supposed  light  to 
be  made  up  of  minute  particles  darting  out  from  the  sun  and 
every  light-giving  body.  Huyghens,  on  the  contrary,  taught 
that  light  is  produced  by  the  vibrations  or  waves  of  an  in- 
visible ether  which  is  supposed  to  fill  all  space.  This  was 
called  the  Undulatory  or  Wave  Theory. 

Newton's  authority  was  so  great,  and  the  experiments  he 
made  to  prove  his  theory  were  so  striking,  that  the  *  Corpus- 
cular theory '  was  generally  received  as  the  true  one,  espe- 
cially as  Huyghens  had  only  made  a  few  simple  experiments 
in  support  of  his  idea ;  and  it  was  more  than  a  hundred 
years  after  Huyghens  first  published  his  '  Treatise  on  Light ' 
before  a  man  arose  to  defend  the  Undulatory  theory  and  to 
bring  it  again  into  notice.  This  man  was  Dr.  Thomas  Young, 
the  first  Professor  of  Natural  Philsophy  at  the  Royal  Insti- 
tution of  London. 

Thomas  Young,  who  was  the  son  of  a  Quaker,  was  born 
at  Milverton,  in  Somersetshire,  in  1773,  ^"^^  died  in  1829. 
He  was  brought  up  at  home,  and  seems  to  have  been  a  very 
clever  lad,  for  he  knew  seven  languages  at  the  age  of  four- 
teen, besides  having  studied  Natural  Science  as  an  amuse- 
ment. He  then  went  to  the  Edinburgh  University,  where  he 
worked  under  dear  old  Dr.  Black,  whose  enthusiasm,  no 
doubt,  helped  much  to  increase  his  love  of  science.  When  he 
was  only  twenty  he  sent  a  paper  on  '  Vision '  to  the  Royal 
Society,  and  was  elected  a  member  the  following  year.  He 
then  went  to  Cambridge  in  order  to  be  able  to  satisfy  the 
College  of  Physicians,  and  practised  as  a  medical  man  in 
London,  where,  in  1801,  he  was  also  made  Professor  of 
Natural  Philosophy  at  the  Royal  Institution,  which  had  just 
been  founded,  and  Editor  of  the  Nautical  Almanack     He  is 


304  NINETEENTH  CENTURY,  pt.  iii. 

very  famous  as  one  of  the  first  men  who  deciphered  the 
Egyptian  hieroglyphical  writings,  and  yo.u  will  often  hear 
him  mentioned  as  an  Egyptian  scholar  \  but  what  we  have 
now  to  consider  are  his  discoveries  about  Light. 

Young  tells  us  himself  that  it  was  in  May  1801  that  he 
first  made  an  experiment  which  seemed  to  him  to  prove 
that  light  must  be  a  succession  of  tiny  waves  moving  across 
space  as  Huyghens  had  supposed.  His  experiment  was  the 
following.  He  made  a  hole  in  the  window-shutter  of  a 
dark  room,  and  covered  it  with  a  piece  of  thick  paper,  in 
which  he  had  pricked  a  small  hole  with  a  needle.  He  then 
put  a  small  looking-glass  outside  the  shutter,  so  as  to  throw 
the  sunlight  very  fully  upon  the  hole  and  send  a  cone  of 
spreading  light  through  it.  In  this  cone  of  Hght  he  held  a 
very  narrow  strip  of  card  and  watched  the  shadow  which  it 
threw  on  the  wall,  or  on  another  piece  of  card  behind  it. 
On  each  side  of  the  shadow  there  were  some  faint  fringes  of 
colour,  but  besides  these  he  saw  in  the  shadow  //i"^^  dark  and 
light  upright  bands,  which  finished  off  in  a  faint  white  band 
in  the  middle  of  the  shadoAv.  It  was  from  these  faint  bands, 
which  many  men  would  have  thought  not  worth  noticing, 
that  Young  worked  out  the  truth  of  the  Wave  Theoiy  of 
Light. 

The  first  question  he  asked  himself  was — '  Why  should 
there  be  any  light  at  all  in  the  shadow  ? '  This  was  not 
difficult  to  answer,  for  as  light  travels  in  all  directions,  a  part 
of  it,  passing  on  each  side  of  the  strip  of  card,  will  spread 
out  behind  it.  But  why  should  this  light  arrange  itself  in 
stripes  and  not  fall  equally  all  over  the  shadow  ?  It  seemed 
at  first  impossible  to  explain  this;  but  when  Young  placed 
his  hand  so  as  to  prevent  the  light  passing  along  one  of  the 
edges  of  the  card  he  found  that  the  fi'inges  or  bands  dis- 


CH.  XXXII.  INTERFERENCE   OF  LIGHT.  305 

appeared  enth'ely^  and  when  he  took  away  his  hand  they 
returned.  It  was  clear,  then,  that  so  long  as  the  Hght  passed 
in  one  direction  only  behind  the  card  it  spreads  itself  out 
equally,  but  directly  the  two  sets  of  rays  from  the  two  sides 
met  each  other,  dark  and  light  bands  appeared. 

Now  Newton's  emission  theory  would  give  no  explana- 
tion of  this  curious  fact,  for  if  light  were  made  of  tiny  par- 
ticles there  is  no  reason  why  these  particles  in  crossing  each 
other  should  make  dark  bands.  On  the  contrary,  the  more 
of  them  there  were  the  more  light  there  ought  to  be.  The 
Undulatory  or  Wave  Theory,  however,  explained  the  bands 
perfectly,  and  this  we  must  now  try  to  understand. 

You  will  remember  that  Huyghens  supposed  an  ether 
filling  all  space  to  be  set  in  motion  by  the  sun,  or  any  other 
luminous  body,  and  to  heave  up  and  down  in  tiny  waves  just 
as  the  sea  heaves,  or  the  water  of  a  pond  when  you  agitate  it. 

Suppose,  therefore,  that  a  number  of  waves  of  water,  all 
of  the  same  size,  are  moving  along  one  side  of  a  lake  as  at  a, 
Fig.  48,  p.  306,  and  flowing  out  through  a  narrow  channel  at 
the  end,  and  suppose  another  set  of  waves  to  be  moving  along 
the  other  side,  b,  so  that  the  two  sets  meet  at  the  mouth  of  the 
channel.  Then,  if  the  two  waves  c  and  d  are  both  rising  up 
when  they  meet,  they  will  join  together  into  one  large  wave, 
and  will  continue  to  flow  in  large  waves  down  the  channel. 
But  if  they  meet,  as  in  Fig.  49,  when  c  is  falling  and  d  is 
rising,  then  c  will  flow  into  the  hollow  of  d  and  fill  it  up, 
and  instead  of  a  large  wave  being  made,  the  surface  of  the 
water  will  become  smooth. 

Now  Young  pointed  out  that  this  is  exactly  what  happens 
to  the  undulations  of  light.  After  passing  through  the  hole 
in  the  shutter,  they  move  on  till  they  come  to  the  card,  and 
here  they  wheel  round  each   edge   of  the  card  and  meet 


;o6 


NINETEENTH  CENTURY. 


PT.  III. 


behind  it.  Those  which  meet  in  the  middle  of  the  shadow 
have  each  travelled  exactly  the  same  distance  with  the  same 
number  of  waves,  so  they  meet  as  in  Fig.  48,  and  a  strong 
undulation  is  produced,  causing  a  band  of  light.  But  on 
either  side  of  the  exact  middle  the  rays  will  not  have  tra- 
velled exactly  the  same  distance,  but  one  will  have  made 
half  a  wave  more  than  the  other,  so  they  will  meet  as  in  Fig. 
49,  and  destroy  each  other,  causing  a  band  of  darkness. 
Outside  these  again  the  ray  which  has  come  the  longer  dis- 

FlG.  48. 


Fig.  49, 


Diagrams  illustrating  the  Interference  of  Waves. 

In  Fig.  48  the  waves,  c  d,  meet  in  the  same  phase,  and  produce  strong  undulations. 
In  Fig.  49  the  waves,  c  d,  meet  in  the  opposite  phase,  and'  interfere  with  each 
other. 

tance  has  had  time  to  make  up  another  half-wave,  so  it  meets 
the  other  ray  as  a  friend  again,  and  both  of  them  rising 
together,  a  strong  wave  and  a  light  band  is  the  result.  In 
this  way  they  go  on,  first  helping  and  then  interfering  with 
each  other,  and  thus  making  alternate  bands  of  light  and 
darkness  across  the  shadow.  For  this  reason  Young  called 
his  discovery  the  *  Interference  of  light* 


CH.  XXXII.    COLOURS   CAUSED  BY  INTERFERENCE,    307 

If  this  experiment  is  made  with  light  of  one  colour  only, 
as,  for  example,  with  light  which  has  been  passed  through 
red  glass,  and  so  is  composed  only  of  red  rays,  then  the 
bands  are  simply  dark  and  light.  But  if  sunlight  is  used 
another  curious  effect  is  seen,  namely,  the  bands  are  faintly 
tinged  with  the  colours  of  the  rainbow  \  and  this  too  Young 
showed  to  be  beautifully  explained  by  the  Undulatory  Theory. 
It  was  stated  at  p.  177  that  the  colour  of  the  light  which 
reaches  our  eye  depends  upon  the  rapidity  of  the  vibrations 
of  the  ether,  just  as  the  sound  of  a  note  upon  our  ear 
depends  upon  the  rapidity  of  the  vibrations  of  the  air. 
Consequently  the  waves  of  the  prismatic  colours  are  of 
different  lengths,  so  that  when  the  two  rays  of  light  meet 
behind  the  card  the  waves  of  the  various  colours  do  not 
all  arrive  together.  For  example,  those  waves  which  cause 
us  to  see  the  colour  violet  are  much  shorter  and  more 
rapid  than  those  which  cause  us  to  see  red.  Therefore, 
when  the  red  waves  meet  each  other  as  friends  (as  in 
Fig.  48),  and  make  a  strong  vibration,  the  violet  ones  will 
meet  each  other  as  foes  (as  in  Fig.  49),  and  interfere  with 
each  other ;  and  so  we  shall  see  a  bright  red  stripe  made  by 
the  strong  red  wave,  while  the  violet  waves  will  be  destroyed 
A  little  farther  on  the  violet  waves  will  meet  as  friends,  and 
then  we  see  a  violet  streak,  while  the  red  ones  will  in  their 
turn  be  destroyed. 

Colours  on  the  Soap-bubble. — The  beautiful  colours  of 
the  soap-bubble  are  caused  in  this  way,  and  an  explanation 
of  them  will  help  you  to  picture  to  yourself  this  effect  of  the 
interference  of  light.  If  you  have  ever  blown  a  well- shaped 
soap-bubble,  and  watched  it  settle  down  quietly  where  there 
is  no  wind  to  disturb  it,  you  cannot  fail  to  have  noticed  the 
colours  which  appear  upon  it.     If  the  bubble  is  very  perfect 


3o8 


NINETEENTH  CENTURY. 


PT.   III. 


these  colours  arrange  themselves  in  rings,  beginning  with  a 
dark  spot  at  the  top  of  the  bubble  and  forming  alternate 
bands  of  blue,  yellow,  orange,  and  red,  which  grow  fainter 
and  fainter  down  the  sides  of  the  bubble  till  they  dis- 
appear. The  reason  of  these  colours  is  that,  when  the 
sunlight  falls  on  the  thin  film  of  the  bubble,  a  little  of  the 
light  is  reflected  straight  back  to  the  eye  from  the  surface  <7, 
Fig.  50  j  but  most  of  it  passes  on  to  the  second  surface  ^, 
and  there  again  some  is  reflected,  so  that  two  sets  of  waves 
are  constantly  reaching  the  eye,  one  from  a  and  one  from  b. 
These  two  sets  meet  before  they  come  to  our  eye,  and  we 
have  just  seen  (p.  306)  that  it  depends  entirely  how  they 
meet  whether  we  see  light  or  darkness. 

Suppose  the  film  is  just  thick  enough  for  the  two  rays  to 


Fig.  so. 


^y^ 


Reflection  of  Light  from  the  two  surfaces  of  a  Soap-bubble.' 

R,  Ray  of  light,  part  of  which  is  reflected  from  the  surface  a,  and  part  from  the 
inner  surface,  b,  to  the  eye. 

meet  when  the  red  waves  of  each  are  7-isi7ig ;  we  shall  then 
have  a  full  red  wave  upon  our  eye.     But  in  that  case,  as  the 

'  The  film  of  a  soap-bubble  is  really  only  the  thickness  of  a  fine 
line  even  in  the  thickest  part ;  but  it  was  necessary  to  exaggerate  the 
two  surfaces  in  the  diagram  to  show  the  passage  of  the  ray  of  light. 


CH.  XXXII.  MALUS   ON  POLARIZATION.  309 

violet  waves  are  a  different  length,  they  will  not  have  met  as 
friends,  but  as  foes,  one  up  and  the  other  down,  and  will 
destroy  each  other  ;  and  so  will  the  waves  of  all  the  other 
colours,  because  they  are  not  of  the  same  length  as  the  red 
waves.  Therefore  the  only  impression  on  our  eye  will  be 
that  of  red.  But  the  bubble  is  always  growing  gradually 
thicker  down  its  sides  because  the  soapy  liquid  is  creeping 
downwards.  So  a  little  lower  down  the  red  waves  from  the 
two  surfaces  «  and  b  will  no  longer  fit  each  other,  but  will 
meet  unevenly  and  the  red  colour  v/ill  be  destroyed.  It  will 
now  be  the  turn  of  the  violet  rays  to  combine  and  make  a 
strong  wave  to  our  eye  \  a  little  lower  down  it  will  be  the 
turn  of  the  green  waves,  then  of  the  yellow,  and  then  the 
film  will  be  thick  enough  for  the  red  wa^es  to  come  together 
again,  and  so  it  will  go  on  ;  each  colour  in  its  turn  will  pro- 
duce a  strong  wave,  while  all  the  others  are  quenched,  until 
the  film  is  too  thick  for  the  effect  to  be  produced. 

This  is  a  very  rough  idea  of  the  way  in  which  the  Undu- 
latory  Theory  explains  the  colours  which  we  see  in  shadows 
and  in  the  soap-bubble.  When  you  study  the  subject  of 
light  you  will  see  how  very  complicated  these  wave  move- 
ments really  are ;  but  without  special  knowledge  you  cannot 
understand  more  than  I  have  given  you  here.  The  colours 
on  mother-of-pearl,  on  a  duck's  neck,  on'  the  transparent 
wings  of  insects,  and  even  on  the  scum  floating  on  a  pond, 
are  all  produced  by  the  interference  of  light,  and  we  owe 
the  discovery  of  this  simple  and  beautiful  explanation  to 
Dr.  Thomas  Young. 

Malus  discovers  the  Polarization  of  Light  by  Reflection, 
1808. — The  next  step  in  the  science  of  light  was  made  by 
Etienne  Louis  Malus,  a  young  French  engineer  officer,  who 
was  born  in  1775,    and  died  in  181 2,  when  he  was  only 


3IO  NINETEENTH  CENTURY.  pt.  hi. 

thirty- seven  years  of  age.  He  was  a  most  accomplished 
mathematician,  and  if  he  had  lived  longer  would  probably 
have  been  one  of  the  most  celebrated  men  of  our  century. 

You  will  remember  that  in  1669  a  Danish  physician 
named  Bartholinus  discovered  that  a  ray  of  light  is  split 
into  two  rays  in  passing  through  Iceland  spar  in  any  direc- 
tion except  along  the  axis  of  the  crystal ;  and  that  Huyghens 
explained  this  by  saying  that  the  crystal  was  more  elastic  in 
one  direction  than  in  another,  so  that  the  waves  moved  at 
different  rates  through  it  (see  p.  180).  To  understand 
Malus's  discovery  you  must  also  remember  that  one  of 
these  divided  rays,  if  it  falls  upon  a  second  crystal  in  the 
same  manner  as  the  first,  goes  on  its  way  as  a  single  ray, 
but  if  the  second  crystal  is  turned  round  a  little  the  ray  splits 
up  again  into  two  rays,  one  much  blighter  than  the  other. 

In  the  year  1808,  M.  Malus  was  standing  at  his  study 
window  in  the  Rue  d'Enfer,  in  Paris,  looking  through  a 
prism  of  Iceland  spar  at  the  sunlight  reflected  from  the 
windows  of  the  Luxembourg  Palace,  which  stood  opposite. 
All  at  once  he  observed  to  his  surprise  that  he  saw  only  one 
image  through  the  prism  instead  of  two.  Turning  his  prism 
a  little,  he  got  the  two  images  again,  but  one  was  much 
brighter  than  the  other,  and  when  he  turned  the  crystal  a 
little  farther  the  other  image  disappeared,  and  he  had  only 
one  again.  In  fact,  the  light  which  was  reflected  from  the 
window  at  one  particular  angle  (56°  45')  behaved  just  like 
one  of  the  divided  rays  which  has  come  out  of  a  crystal,  and 
not  like  an  ordinary  ray  which  comes  from  the  sun. 

This  remarkable  peculiarity  puzzled  Malus  greatly,  and 
led  him  to  make  a  great  many  experiments,  by  which  he  dis- 
covered that,  whenever  light  is  reflected  from  glass  at  this 
particular  angle  of  56°  45',  it  has  the  peculiar  characters  of  a 


CH.  XXXII.      THE  POLARIZATION  OF  LIGHT.  311 

divided  ray  which  has  passed  through  Iceland  spar.  Light 
reflected  from  other  substances  is  also  divided  up  in  this 
way,  only  the  angle  at  which  this  change  takes  place  is  dif- 
ferent for  each  different  substance.  Malus  was  the  first  to 
call  this  peculiar  tf^Qct  polarization,  and  light  which  behaves 
in  this  way  has  since  been  always  called  '  polarized  light.' 

His  discovery  led  to  a  completely  new  study,  for  people 
had  almost  forgotten  the  experiments  which  had  been  made 
by  Huyghens  more  than  100  years  before  j  but  this  novel  and 
curious  fact  attracted  attention,  and  the  subject  was  taken  up 
again.  Malus  did  not  live  to  explain  the  matter  ;  he  found 
out  many  remarkable  facts  about  it,  but  it  was  Young  and 
the  French  philosopher  Fresnel  who  really  worked  out  the 
theory  of  the  polarization  of  light. 

Polarization  of  Light  explained  by  Young  and  Fresnel. 
1816. — Augustin  Fresnel,  the  contemporary  and  friend  of 
Thomas  Young,  was  bom  at  Broglie,  in  France,  in  1788. 
He  was  a  delicate  backward  boy,  who  disliked  books,  but 
loved  practical  experiments,  and  he  followed  his  tastes  by 
becoming  an  engineer.  Being  a  Royalist,  however,  he  was 
harshly  treated  by  the  Emperor  Napoleon  I.,  and  he  retired 
to  Normandy  to  devote  himself  to  science.  He  died  of 
consumption  in  1827. 

It  is  very  difficult  to  decide  whether  Young  or  Fresnel 
was  the  first  to  point  out  how  certain  peculiar  vibrations  of 
the  ether  explain  the  polarization  of  light.  But  fortunately 
this  need  not  trouble  us,  for  the  men  themselves  were  not 
anxious  to  dispute  about  their  claims.  Young's  discoveries 
were  very  coldly  received  in  England,  for  very  few  men  un- 
derstood them  j  and  unfortunately  Lord  Brougham  wrote 
many  severe  articles  against  them  in  the '  Edinburgh  Review,' 
which  made  people  think  they  were  only  foolish  specula- 


312  NINETEENTH  CENTURY.  pt.  hi. 

tions.  But  in  France  two  men,  Fresnel  and  his  friend  M. 
Arago,  understood  and  valued  Young's  labours  as  soon  as 
they  heard  of  them,  and  from  that  time  the  three  men  helped 
each  other  in  every  way  without  the  least  jealousy  as  to  who 
should  have  the  credit  of  the  work. 

Fresnel  had  puzzled  out  the  question  of  the  *  Interference 
of  Light'  before  he  heard  that  Young  had  done  so  too;  and 
it  happened  that  while  Fresnel  and  Arago  were  one  day 
making  experiments  upon  the  way  in  which  waves  of  light 
interfere  with  each  other,  they  found  that  the  ordinary  and 
extraordinary  rays  coming  out  of  crystal  and  Iceland  spar 
would  not  interfe7'e  with  or  quench  each  other,  as  two  ordi- 
nary rays  do.  (See  p.  306.)  This  led  Fresnel  to  suspect  that 
the  waves  in  the  two  rays  must  move  in  a  different  manner. 
He  wrote  this  to  Dr.  Young,  and  found  that  he  also  had  the 
same  idea,  and  this  led  to  a  number  of  experiments,  by 
which  they  proved  at  last  that  the  waves  in  a  natural  ray  of 
light  do  not  move  merely  up  and  down  like  waves  in  a  pond, 
but  also  from  side  to  side ;  and  that  when  light  is  polarised 
this  complex  vibration  is  destroyed  and  the  waves  of  each 
separate  ray  move  only  in  one  direction. 

To  understand  this,  take  a  piece  of  string,  and,  fastening 
one  end  to  the  wall,  hold  the  other  end  in  your  hand.  If  you 
now  move  your  hand  up  and  down,  you  will  make  waves  in 
the  string  which  will  point  up  to  the  ceiling  and  down  to  the 
ground,  making  what  are  called  vertical  vibrations  (a.  Fig.  51). 
Stop  this  movement,  and  then  move  your  hand  from  side  to 
side  ;  the  waves  will  now  point  from  wall  to  wall  in  horizon- 
tal vibrations  (b,  Fig.  51).  If  you  then  move  your  hand  so 
that  it  points  to  the  ceiling  to  your  right,  and  the  floor  to 
your  left,  you  get  waves  between  the  two  others,  and  so  you 
can  go  on  varying  the  position  of  the  waves  in  all  directions  ; 


CH.  XXXII.    VERTICAL  ^  HORIZONTAL  VIBRATIONS.    313 


or,  in  scientific  language,  you  cause  the  string  to  vibrate  in 
a  different  plane. 

Now  Young  and  Fresnel  proved  that  a  natural  ray  of 
light  is  composed  of  all  these  different  waves  moving  at 
the  same  time,  some  up  and  down,  some  from  side  to 
side,  and  some  between  the  two.  But  when  the  light 
passes  through  a  piece  of  Iceland  spar,  there  are  two  and 
only  two  ways  in  which  the  waves  can  move  :  one  up  and 
down— and  along  this  path  one  ray  of  light  goes ;  the 
other  from  side  to  side — and  along  this  the  other  ray  goes, 
and  so  they  become  divided. 

You  can  imitate  this  by  passing  your  string  through  a 
card-  with  a  straight  slit  in  it.  Place  the  card  upright,  as 
at  A,  Fig.  51,  and   it  is    clear   that  the   waves  will  be  up 


fc*  Diagram  illustrating  the  passage  of  Waves  of  Light  through  a  Crystal. 

A,  Waves  moving  in  a  vertical  plane.     B,  Waves  moving  in  a  horizontal  plane. 

and  down ;  place  it  sideways,  as  at  B,  ^nd  the  waves  will 
be  from  side  to  side.  These  two  positions  of  the  card 
imitate  the  two  paths  of  a  ray  of  light  through  a  crystal, 
and  they  show  how  the  difference  in  the  peculiarities  of 
the  divided  rays  is  caused  by  their  moving  in  a  different 
plane. 

We  cannot  follow  this  out  more  completely  in  a  history, 
15 


314  NINETEENTH  CENTURY.  pt.  hi. 

for  the  polarization  of  light  is  a  very  difficult  subject ;  but 
this  was  the  first  step  made  in  it.  Fresnel  afterwards 
worked  out  accurately  why,  when  light  is  reflected  at  a  cer- 
tain angle,  the  vibrations  are  all  made  to  move  in  one  plane, 
and  so  the  light  is  polarized,  as  Malus  had  found  it  to  be 
from  the  surface  of  the  Luxembourg  windows.  He  also 
showed  how  in  some  crystals,  as  in  quartz  crystals,  the  waves 
are  made  to  act  upon  each  other,  so  that,  instead  of  moving 
to  and  fro,  they  wind  round  and  round  like  the  wire  of  a 
corkscrew.  These  and  many  other  experiments,  as  for  ex- 
ample, those  upon  the  beautiful  colours  caused  by  polariza- 
tion, were  carried  much  farther  by  the  eminent  French 
chemist,  M.  Biot  (born  1774,  died  1862),  and  by  Sir  David 
Brewster  (bom  1784,  died  1868),  but  they  are  too  long  and 
difficult  to  be  explained  here.  As  I  said  at  the  beginning 
of  this  chapter,  the  '  Theory  of  Light '  requires  a  special 
study,  and  if  you  have  understood  something  of  the  move- 
ment of  the  supposed  ether  waves — how  they  can  interfere 
with  each  other  and  produce  light  or  darkness,  how  they 
produce  coloured  rings  in  the  soap-bubble,  and  how  their 
vibrations  are  altered  in  passing  through  a  crystal  or  in  re- 
flection at  certain  angles — ^you  have  learnt  as  much  as  can  be 
easily  grasped  of  the  discoveries  of  Young  and  Fresnel. 


Chief  Works  consulted.  — Young's  *  Lectures  on  Natural  Philosophy,' 
1845;  Peacock's  'Life  and  Works  of  Young;'  Arago's  *Eloge  of 
Fresnel;'  Herschel's  'Lectures  on  Familiar  Subjects ; '  Tyndall,  'On 
Light ; '  Spottiswoode's  '  Polarization  of  Light  ; '  Wliewell's  *  Inductive 
Sciences  ; '   '  Encyclopaedia  Britannica ' — Sixth  Dissertation. 


cii.  xxxiir.  SPECTRUM  ANALYSIS,  315 


CHAPTER  XXXIIL 

SCIENCE    OF   THE   NINETEENTH   CENTURY   (CONTINUED). 

History  of  Spectrum  Analysis — Discovery  of  Heat-rays  by  Sir  W, 
Herschel — And  of  Chemical  Rays  by  Ritter  of  Jena — Photography 
first  suggested  by  Davy  and  Wedgwood — Carried  out  by  Daguerre 
and  Talbot — Dark  Lines  in  the  Spectrum  first  observed  by  Wollaston 
— Mapped  by  Fraunhofer — Life  of  Fraunhofer — He  discovers  that 
the  Dark  Lines  are  different  in  Sun-light  and  Star-light — Experi- 
ments on  the  Spectrum  of  different  Flames — Four  new  Metals  dis- 
covered by  Spectrum  Analysis — Bunsen  and  Kirchhoff  explain  the 
Dark  Lines  in  the  Solar  Spectrum — Metals  in  the  Atmosphere  of 
the  Sun — Huggins  and  Miller  examine  the  Stars  and  Nebulae  by 
Spectrum  Analysis. 

History  of  Spectrum  Analysis,  1800-1861. — We  now 

come  to  the  history  of  Spectrum  analysis^  or  the  study  of 
the  various  coloured  bands  produced  by  different  kinds  of 
light  when  seen  through  a  prism.  This  is  certainly  one  of 
the  most  wonderful  discoveries  of  our  century,  and  though 
its  history  is  difficult,  partly  because  it  belongs  to  our  own 
time  and  is  going  on  even  now,  yet  we  may  learn  something 
about  it.  The  first  step  was  made,  as  you  will  remember, 
when  Newton  discovered  that  white  light  is  composed  of 
different  coloured  rays,  but  even  he  little  suspected  what 
histories  those  rays  could  be  made  to  tell. 

Discovery  of  Heat-rays  by  Sir  William  Herschel,  1800. 
— One  of  the  first  facts  which  was  learnt  in  this  century  about 
the  spectrum  was,  that  the  coloured  band  which  is  seen 
when  a  ray  of  white  light  is  passed  through  a  prism  does  not 


3i6  NINETEENTH  CENTURY.  pt.  hi. 

give  us  the  whole  of  the  dispersed  ray ;  for  there  are  many- 
invisible  rays  at  both  ends  of  the  coloured  part  which  are 
very  active,  though  we  cannot  see  them. 

It  had  alway^s  been  thought  that  the  hottest  rays  must  be 
those,  such  as  the  yellow  ones,  which  give  the  most  light,  and 
in  the  year  1800  Sir  William  Herschel,  wishing  to  try  this, 
took  a  thermometer  and  passed  it  gradually  from  one  end 
to  the  other  of  the  coloured  band.  The  result  was  curious. 
He  began  at  the  violet  end  of  the  spectrum  (Plate  I.  No.  i, 
p.  320),  and,  as  he  expected,  the  thermometer  rose  higher 
and  higher  as  he  approached  the  yellow  part ;  but  to  his 
surprise  it  did  not  stop  here.  When  he  passed  on  through 
the  yellow  into  the  red,  the  heat  still  increased,  and  even 
became  more  intense  as  he  passed  out  of  the  coloured  band 
altogether  into  the  darkness  beyond.  By  this  experiment  he 
found  that  the  heat-rays  extend  for  some  distance  beyond 
the  red  colour,  and  that  they  are  strongest  in  that  part  where 
no  light  is  to  be  seen. 

Discovery  of  Chemical  Rays  by  Hitter,  1801. — Soon 
after  Sir  William  Herschel  had  discovered  the  dark  heat- 
rays,  a  still  more  remarkable  fact  was  brought  to  light  about 
the  violet  end  of  the  spectrum.  The  Danish  chemist  Scheele, 
who  you  will  remember  as  one  of  the  discoverers  of  oxygen 
(see  p.  232),  had  once  remarked  that  nitrate  of  silver  will 
turn  black  if  the  violet  rays  of  a  spectrum  are  thrown  upon 
it.  In  1 80 1,  Professor  Ritter,  of  Jena,  was  repeating  this 
experiment,  and  he  found  that  the  black  patches  appeared 
slightly  on  those  parts  of  the  paper  where  the  violet  rays 
fell,  but  very  strongly  indeed  beyond  those  rays  where  the 
spectrum  was  quite  dark.  So  that  at  this  end  also  there  are 
invisible  rays,  and  these  have  the  extraordinary  power  of  de- 
composing or  breaking  up  nitrate  of  silver,  and  some  other 


CH.  XXXIII.  PHOTOGRAPHY.  317 

substances,  so  as  to   leave   distinct   marks  upon  anything 
touched  by  them. 

Photography. — You  will  see  at  once  that  this  is  the 
secret  of  Photography.  In  1802,  Sir  Humphry  Davy  and 
Dr.  Thomas  Wedgw^ood  suggested  that  pictures  might  be 
taken  in  this  way  by  the  rays  of  the  sun  acting  upon  chloride 
of  silver,  and  they  even  succeeded  in  making  some.  But 
they  could  not  prevent  them  from  fading  away  again,  and 
it  was  not  until  1839  that  a  Frenchman  named  Daguerre 
learnt  how  to  fix  the  pictures  so  that  they  would  remain,  and 
Mr.  Fox  Talbot  afterwards  improved  the  process.  We  can- 
not enter  here  into  a  complete  account  of  photography,  but 
you  may  form  some  idea  of  how  the  rays  of  light  produce  a 
picture. 

When  you  go  to  have  your  photograph  taken,  the  glass 
plate  which  is  to  receive  your  picture  has  been  bathed  in 
nitrate  of  silver,  with  some  other  chemicals.  When  you 
stand  in  front  of  it  and  it  is  uncovered,  a  luminous  image 
of  your  face  or  body,  which  has  been  brought  to  a  focus 
on  the  lens  of  the  camera,  falls  upon  the  plate,  and  the  che- 
mical rays  (which  are  chiefly  those  beyond  the  violet  end  of 
the  spectrum)  decompose  the  nitrate  of  silver.  You  can 
see  nothing  when  the  plate  is  taken  out  of  the  box  in  which 
it  was  placed,  but  by  pouring  some  more  chemicals  called 
protosulphite  of  iron  and  pyrogallic  acid  upon  it,  the  parts 
which  the  light  has  touched  all  start  out  in  different  shades, 
exactly  in  proportion  as  the  chemical  waves  of  light  have 
fallen  upon  it  strongly  or  feebly.  It  will  be  exactly  the 
opposite  to  your  real  appearance,  because  where  most  light 
has  fallen,  there  the  chemicals  will  be  most  decomposed  and 
will  leave  the  blackest  tints. 

Another   fluid   called   hyposulphite   of   sodium  is  now 


3i8  NINETEENTH  CENTURY.  PT.  ill. 

poured  upon  the  plate  to  melt  away  any  nitrate  of  silver 
which  remains,  so  that  when  the  sun  next  falls  upon  it  it 
may  not  blacken  the  rest  of  the  plate  and  destroy  the 
picture.  Then  the  glass  plate  is  again  placed  in  the  sun 
with  properly  prepared  paper  under  it ;  and  now  the  shades 
are  reversed.  Under  the  dark  parts  of  the  plate  the  sun 
will  act  feebly  on  the  paper,  and  produce  light  patches, 
while  through  the  light  parts  it  will  act  strongly  and  produce 
shadows.  And  in  this  way  the  lights  and  shades  of  your 
image  will  appear  in  their  right  places  on  the  paper.  All 
this  work  is  done  by  the  chemical  rays  which  are  chiefly  at 
and  beyond  the  violet  end  of  the  spectrum,  and  this  explains 
why  bright  red  and  yello\y  objects  come  out  dark  in  a  photo- 
graph, because  these  colours  contain  so  i<s.y{  chemical  rays, 
while  the  darkest  blue  and  violet  come  out  nearly  white, 
because  they  act  strongly  upon  the  nitrate  of  silver. 

WoUaston  first  observes  the  Dark  Lines  in  the  Spectrum, 
1802. — In  the  same  year  that  Ritter  discovered  the  chemi- 
cal rays  at  the  dark  end  of  the  spectrum  which  have  given 
us  the  whole  art  of  photography,  Dr.  WoUaston,  one  of 
our  most  celebrated  chemists  (born  1766,  died  1828),  first 
saw  the  dark  lines  in  the  spectrum  which  have  enabled  us  to 
discover  the  actual  materials  which  exist  in  the  sun  and 
stars.  Dr.  WoUaston,  who  made  many  good  experiments 
on  light,  was  one  day  examining  ordinary  daylight  through 
a  prism,  and  instead  of  letting  in  the  light  by  a  round  hole 
in  the  shutter  as  Newton  had  done,  he  made  only  a  very  thin 
slit,  so  that  the  colours  of  the  spectrum  were  prevented  from 
overlapping  each  other,  as  they  had  done  in  Newton's  expe- 
riment. The  result  was  that  seven  dark  upright  lines  or 
spaces  appeared  in  the  band  of  colour,  which  seemed  to  show 
that  no  light  fell  on  those  parts.  WoUaston  did  notliing  more 


CH.  XXXIII.       FRAUNHOFERS  DISCOVERIES.  319 

than  point  out  the  existence  of  these  Hnes  j  but  in  181 4 
Fraunhofer,  a  German  optician,  who  had  heard  nothing  of 
Wollaston's  experiment,  discovered  them  over  again  inde- 
pendently, and  learnt  more  about  them. 

Fraunhofer,  1787-1826.— Joseph  Fraunhofer,  the  son 
of  a  glazier,  was  born  in  1787,  at  Straubing,  in  Bavaria. 
Being  left  an  orphan  when  quite  young,  he  was  apprenticed 
to  a  glass  manufacturer,  who  kept  him  hard  at  work  all  day. 
But  he  longed  so  much  for  knowledge  that  he  borrowed 
some  old  books  and  spent  his  nights  in  learning.  In  the 
year  1801  the  house  in  which  he  lived  fell  down  one  night 
and  killed  all  the  people  in  it  except  young  Fraunhofer, 
and  his  cries  being  heard  by  the  people  outside,  they  set  to 
work  to  try  and  release  him.  It  happened  that  Maximilian 
Joseph,  Elector  of  Bavaria,  came  to  see  the  accident,  and 
he  encouraged  the  workmen  so  much,  that  in  four  hours  the 
young  man  was  dug  out,  wounded,  but  alive.  The  Elector 
was  so  much  interested  in  this  narrow  escape,  that  he  gave 
Fraunhofer  eighteen  ducats,  and  the  lad  used  the  money  to 
buy  himself  off  from  his  apprenticeship  in  order  to  have 
some  free  time  for  study.  After  this  he  lived  by  polishing 
lenses,  and  he  worked  so  well  that  he  soon  became  the 
master  of  a  business,  and  was  able  to  spend  his  spare  time 
in  the  study  of  Physics  and  Astronomy,  which  he  loved  pas- 
sionately. Finally  he  became  manager  of  the  physical 
laboratory  of  an  academy  in  the  town  of  Benedictbaiern, 
near  Munich.  " 

Fraunhofer's  Discoveries  about  the  Spectrum,  1814. — 
From  having  been  constantly  at  work  as  an  optician,  Fraun- 
hofer had  been  led  to  study  the  subject  of  light,  and  among 
other  experiments  he  repeated  those  of  Newton;  and  it  hap- 
pened that  he  too  used  a  narrow  slit,  as  Wollaston  had  done. 


320  NINErEENTH  CENTURY.  pt.  hi. 

Thus  he  also  noticed  the  black  lines  which  divided  the 
colours,  and  by  making  his  slit  very  narrow  and  using  prisms 
of  very  pure  glass  he  discovered  in  a  ray  of  sunlight  no  less 
than  576  of  these  black  lines.  Plate  I.,  No.  2,  gives  a  few  of 
the  principal  of  these,  to  which  he  put  letters,  and  which  have 
ever  since  been  called  '  Fraunhofer's  lines.'  As  none  of  these 
lines  appear  when  the  light  of  a  candle  or  lamp  is  passed 
through  a  prism,  Fraunhofer  concluded  that  sunlight  must 
be  defective,  and  some  of  its  coloured  rays  must  be  missing. 
For,  as  numberless  waves  of  coloured  light  are  passing 
tlirough  the  slit  and  the  prism  spreads  them  out  so  that 
each  set  of  waves  makes  an  upright  image  of  the  slit  on  the 
spectrum,  if  any  waves  were  missing  there  would  be  a  dark 
image  of  the  slit  instead  of  a  coloured  one. 

By  far  the  best  way  of  understanding  this  is  to  see  it  for 
yourself  Sir  John  Herschel  says  that  a  little  inexpensive 
instrument  may  be  easily  made  with  a  hollow  tube  of  metal, 
blackened  inside,  a  prism  fixed  in  it,  and  a  metal  plate  with 
a  narrow  slit  fastened  across  the  end  of  the  tube.  I  have 
not  been  able  to  find  so  simple  an  instrument  as  this ;  the 
cheapest  sold  by  Mr.  Browning,  the  famous  spectroscope 
maker,  in  the  Strand,  costs  twenty-two  shillings,  and  with 
this  you  may  see  the  black  lines  clearly  when  you  turn 
it  to  the  sun.  But  if  this  is  not  to  be  had,  you  may  gain 
some  idea  of  the  principle  of  the  dark  lines  by  the  following 
illustration.  Colour  a  strip  of  paper  exactly  like  the  con- 
tinuous spectrum,  No.  i,  Plate  I.,  and  then  cut  it  across  into 
very  narrow  strips  and  place  them  in  order  side  by  side  on  a 
dark  ground  ;  each  strip  will  represent  an  image  of  the  slit, 
and  the  whole  will  be  a  continuous  spectrum  as  before.  But 
now  suppose  one  set  of  waves  to  be  wanting ;  take  out  one 
of  your  strips  and  you  will  have  a  dark  space.     This  repre- 


CH.  XXXIII.     SPECTRA    OF  DIFFERENT  FLAMES.  321 

sents  one  of  the  black  lines  in  the  spectrum  where  a  dark 
image  of  the  slit  is  thrown,  and  if  you  take  out  those  which 
correspond  to  the  lines  in  the  sun  spectrum  No.  2,  you  will 
have  an  illustration  of  '  Fraunhofer's  lines.' 

Fraunhofer  measured  these  black  lines  with  the  greatest 
care,  and  he  found  that  in  every  ray  of  sunlight  they  came 
exactly  in  the  same  places.  Then  he  tried  the  light  of 
the  moon  and  Venus ;  still  the  black  lines  were  the  same, 
for  these  planets,  as  you  know,  only  shine  by  the  light  of 
the  sun.  But,  when  he  turned  his  telescope  to  the  stars 
and  caught  their  light,  he  found  a  difference.  There  were 
dark  lines  in  the  star- spectrum,  but  they  were  not  all  in 
the  same  place  as  those  in  the  sun-spectrum,  as  you  will 
see  if  you  compare  No.  2,  Plate  I.,  with  the  star-spectrum, 
No.  5,  in  which  the  lines  seen  on  the  right-hand  side  of  the 
solar  spectrum  are  entirely  wanting. 

Fraunhofer,  therefore,  argued  in  this  way  ;  If  the  black 
spaces  were  caused  by  some  of  the  waves  being  stopped  in 
coming  through  our  own  atmosphere^  they  would  be  the 
same  in  any  spectrum  wherever  the  light  came  from.  But 
as  these  dark  spaces  are  different  in  the  starlight  from  what 
they  are  in  the  sunlight,  there  must  be  some  real  difference 
between  the  light  of  the  sun  and  the  light  of  the  stars  before  it 
comes  to  us.  This  was  the  first  step  in  the  study  of  the 
heavenly  bodies  by  means  of  spectrum  analysis. 

Experiments  on  the  Spectra  of  different  Flames,  1822. — 
For  more  than  forty-five  years  these  black  lines  remained  a 
complete  puzzle  to  all  who  studied  the  spectrum,  but  in  the 
meantime  Sir  John  Herschel,  Mr.  Fox  Talbot,  Sir  David 
Brewster,  and  others,  had  made  many  valuable  experiments 
upon  the  colours  produced  by  different  burning  lights.  You 
know  already  that  it  is  possible  to  make  coloured  flames  by 


322  NINETEENTH  CENTURY.  PT.  iii. 

burning  certain  substances.  For  instance,  if  you  put  com- 
mon salt  in  a  spirit-flame,  it  will  burn  with  a  yellow  colour, 
while  a  substance  called  nitrate  of  strontium  will  give  a 
brilliant  red  flame,  and  is  used  in  making  red  fire  for  the 
theatres.  Many  other  metals  and  earths,  however,  tinge  the 
flame  so  slightly  that  you  cannot  see  the  colour,  and  it  is 
only  by  passing  the  light  through  a  prism  that  you  can 
detect  it. 

It  had  long  been  known  that  light  from  white-hot  solids 
when  thrown  on  a  prism  produces  a  continuous  spectrum, 
that  is,  a  coloured  band  unbroken  by  any  dark  lines.  A 
white-hot  poker,  for  example,  will  give  the  spectrum  No.  i, 
Plate  I.,  and  so  will  burning  paraffin,  because  it  contains 
solid  atoms  of  carbon.  But  burning  gases  or  vapours  do  not 
give  a  continuous  band  of  colour,  they  only  produce  a  few 
bright  lines,  such  as  those  in  Nos.  3  and  4.  You  can  s'ee 
this  by  looking  at  an  ordinary  gas  flame  through  Browning's 
little  spectroscope. 

Now  there  is  a  remarkable  peculiarity  about  these  bright 
lines  formed  by  gases  or  vapours,  namely  that  they  are 
diffe7-ent  for  the  gas  or  vapour  of  every  different  substance. 
Thus,  if  you  burn  any  substance  containing  sodium,  a  bright 
yellow  stripe  will  appear  as  in  No.  3  ;  while  hydrogen  will 
give  one  red,  one  blue,  and  one  violet  stripe,  as  in  No.  4. 
This  test  is  so  true  and  delicate  that  the  eighteen-millionth 
part  of  a  grain  of  sodium  will  give  the  yellow  line ;  nor  does 
it  matter  if  you  bum  many  substances  together,  for  the 
vapour  of  each  one  will  give  its  own  lines  without  inteifering 
luith  the  others. 

It  was  Sir  John  Herschel  in  1822  who  first  suggested 
that  by  burning  substances  in  a  flame,  and  marking  the  bright 
lines  which  they  produced,  it  would  be  possible  to  detect  the 


CH.  xxxili.  BUNSEN  AND  KIRCHHOFF.  323 

most  minute  quantities  of  any  metal  or  earth  which  they  con- 
tained, and  Mr.  Fox  Talbot  carried  out  this  suggestion  in 
1834.  By  this  means  in  the  course  of  time  spectroscopists, 
or  men  who  made  the  spectrum  their  study,  were  able  to 
map  out  accurately  the  coloured  lines  of  every  known  sub- 
stance ;  and  what  is  still  more  wonderful,  new  metals  were 
actually  discovered  by  the  new  lines  they  threw  on  the  dark 
band.  The  first  of  these  two  new  metals,  called  CcEsium 
and  Rubidium^  were  discovered  by  Bunsen  and  Kirchhoif ; 
the  third,  called  Thallium,  which  throws  a  beautiful  green 
line,  was  found  by  Mr.  Crookes ;  and  the  fourth,  called 
Iridium,  by  Richter  and  Reich.  Thus  you  see  spectrum 
analysis  gives  us  an  entirely  new  and  sure  way  of  analysing, 
or  discovering  the  different  elements  in  any  substance. 

Bunsen  and  Kirchhoff  explain  the  Dark  Lines  in  the 
Sun  Spectrum,  1861. — But  all  this  time  no  one  could  solve 
the  question  of  the  black  lines  in  the  solar  spectrum.  Sir 
David  Brewster  came  very  near  to  it  once,  but  just  failed  to 
hit  upon  the  truth.  ^  At  last,  in  186 1,  only  fourteen  years 
ago,  Bunsen  and  Kirchhoff,  two  celebrated  professors  of 
chemistry  and  physics  at  Heidelberg,  discovered  the  secret. 

These  two  men  had  been  making  a  long  set  of  careful 
experiments  upon  all  the  different  substances  of  our  globe, 
burning  them  and  examining  their  gases  one  by  one,  and 
marking  the  bright  lines  of  each  upon  the  spectrum.  In 
doing  this  they-  did  not  use  one  prism  only  as  Fraunhofer 
had  done,  but  four  (see  Fig.  52,  p.  324),  so  arranged  that 
the  light  coming  in  through  a  slit  at  the  beginning  of  the 

^  Sir  William  Thomson  states  in  his  address  to  the  British  Asso- 
ciation in  1 87 1,  that  Professor  Stokes  gave  the  true  explanation  of 
these  lines  in  his  lectures  at  Cambridge  in  1 85 1,  although  he  did  not 
publish  anything  about  it,  and  his  idea  was  not  generally  known. 


324  NINETEENTH  CENTURY.  rr.  in. 

tube  A,  was  spread  out  more  and  more  through  each  prism 
as  it  passed,  and  fell  in  a  spectrum  on  the  object  glass,  c,  of 
the  telescope  b,  through  which  they  examined  it.  They  soon 
found  that  in  order  to  mark  the  exact  position  of  the  bright 
lines  of  each  gas  upon  the  spectrum,  they  wanted  some 
fixed  measure,  and  it  occurred  to  them  that  the  black  lines 
of  the  solar  spectrum,  which  never  change,  would  make  a 
good  scale  with  which  to  compare  all  the  others.  So  they 
arranged  their  spectroscope  in  such  a  manner  that  one-half 
of  the  slit  was  lighted  by  the  sun  and  the  other  half  by  the 

Fig.  52. 


KirchhofF's  Spectroscope  (Roscoe). 

flame  of  a  gas.     In  this  way  No.  2,  Plate  I.,  would  appear 
above,  and  No.  3,  for  example,  immediately  below  it. 

While  doing  this  they  could  not  help  remarking  that  the 
bright  yellow  line  of  the  sodium  spectrum.  No.  3,  was  exactly 
in  the  same  position  as  the  black  line,  d,  in  the  solar  spec- 
trum ;  *  and  Kirchhoff  found  that  when  he  passed  a  faint 
ray  of  sunlight  through  a  flame  of  sodium  (so  as  to  make 

^  These  lines  are  really  double  when  seen  in  a  powerful  spectro- 
scope, but  they  appear  single  in  a  small  instrument. 


CH.  XXXIII.  THE  SOLAR  SPECTRUM.  325 

the  two  spectra,  2  and  3,  cover  each  other),  the  yellow  line 
exactly  filled  up  the  black  line  with  its  light.  He  now 
wished  to  see  how  bright  he  could  make  the  solar  spectrum 
without  overpowering  the  light  of  the  sodium,  so  he  let  the 
full  sunshine  pass  through  the  sodium  flame.  To  his  great 
astonishment  he  saw  the  black  line  at  d  start  out  more 
strongly  than  ever.  The  sodium  flame  had  revenged  itself 
for  being  overpowered  by  absorbing  some  of  the  yellow  light  of 
the  Sim  / 

This  suggested  to  him  the  idea  that  the  black  line  d  must 
be  caused  by  the  white  light  from  the  sun  passing  through 
sodium  vapour  before  it  reaches  us.  There  was  a  very  simple 
way  of  proving  whether  this  were  so  ;  for  burning  solids,  you 
remember,  give  a  continuous  spectrum  (i,  Plate  I.),  there- 
fore, if  he  could  produce  a  dark  line  by  passing  the  light  of 
a  burning  solid  through  sodium  vapour,  he  would  imitate 
one  of  the  defects  in  sunlight.  So  he  burned  a  lime-light, 
and  when  he  had  the  continuous  coloured  band  in  his 
spectroscope,  he  burned  a  sodium  flame  between  the  lime- 
light and  the  prism.  The  experiment  was  quite  successful ; 
the  dark  space,  d,  started  out  upon  the  spectrum,  and  thus 
he  proved  beyond  doubt  that  burning  sodium  vapour  absorbs 
in  white  light  exactly  those  rays  which  it  gives  out  itself  when 
burning. 

He  repeated  the  experiment  with  other  burning  metals, 
such  as  potassium  and  strontium,  and  always  with  the 
same  result.  Each  burning  gas  absorbed  in  the  white  light 
exactly  those  rays  which  it  gave  out  itself  when  burning. 

The  black  lines  on  the  solar  spectrum  were  now  explained, 
for  each  one  of  them  must  imply  that  some  particular  ray  of 
sunlight  has  been  absorbed  by  a  gas  between  the  sun  and 
us,  and  it  must  have  been  absorbed  near  the  sun,  as  Fraun- 


326  NINETEENTH  CENTURY.  n.  ni. 

hofer  had  pointed  out,  because  the  lines  are  different  in 
Hght  which  comes  from  the  stars,  showing  that  in  that  case 
it  has  passed  through  other  kinds  of  gases.  Therefore 
Kirchhoff  concluded  that  round  the  solid  or  liquid  body  of 
the  sun,  which  gives  out  white  light,  and  would  of  itself  pro- 
duce a  continuous  spectrum,  there  must  be  an  atmosphere  of 
gases  of  different  kinds,  which  absorb  or  destroy  particular 
rays  of  light,  and  prevent  them  reaching  us. 

If  this  is  the  case,  it  is  clear  that  we  can  tell  from  the 
lines  in  the  spectrum  what  gases  and  vapours  there  are  in 
this  solar  atmosphere.  For  example,  there  must  be  sodium 
which  cuts  off  the  rays  which  ought  to  come  to  d,  and  there 
must  be  also  iron,  magnesium,  calcium,  chromium,  potas- 
sium, rubidium,  nickel,  barium,  lead,  copper,  zinc,  strontium, 
cadmium,  cobalt,  uranium,  cerium,  vanadium,  palladium, 
aluminium,  titanium,  and  hydrogen,  for  the  bright  Hues  of 
all  these  metals  are  replaced  by  dark  lines  in  the  solar 
spectrum,  showing  that  the  white  light  from  the  body  of  the 
sun  must  have  passed  through  their  gases. 

Dr.  Huggins  and  Dr.  Miller  examine  the  Stars  by 
Spectrum  Analysis,  1862.— Only  a  few  months  after  Kirch- 
hoff had  proved  that  the  black  lines  in  the  solar  spectrum 
reveal  to  us  what  elements  exist  as  gases  around  the  sun, 
two  Enghsh  chemists.  Dr.  Miller,  who  died  a  few  years  ago, 
and  Dr.  Huggins,  who  is  still  living,  began  to  try  the  same 
experiments  with  the  other  heavenly  bodies,  and  the  study 
has  since  been  carried  still  farther  by  Mr.  Lockyer. 

Their  instruments  were  now  much  more  perfect  than 
those  which  Fraunhofer  had  used,  and  they  were  able  to  see 
the  effects  of  our  own  atmosphere  upon  sunlight,  for  when 
the  sun  is  setting  and  its  light  has  to  pass  through  a  long 
layer  of  air  before  it  reaches  us,  faint  lines  appear  on  the 


CH.  xxxiii.  GASEOUS  NEBULA.  327 

spectrum,  because  some  light  is  absorbed  by  the  vapours  in 
our  atmosphere.  Now,  when  Miller  and  Huggins  examined 
the  light  which  comes  from  Jupiter,  they  found  three  or  four 
lines  like  those  caused  by  our  atmosphere,  showing  that 
Jupiter  must  have  an  atmosphere  partly,  but  not  entirely  like 
ours.  Mars  and  Saturn  also  both  showed  these  atmospheric 
lines,  and  so  did  Saturn's  rings,  proving  that  a  similar  atmo- 
sphere must  spread  over  them  also.  But  our  moon  gave  none 
of  them,  and  this  agreed  with  other  evidence  in  showing  that 
the  moon  has  no  atmosphere. 

They  next  passed  on  to  examine  the  light  of  the  stars,  and 
this  was  by  no  means  an  easy  task,  because  the  stars  are  so  far 
off  that  their  light  is  very  faint  and  difficult  to  catch.  Never- 
theless they  proved  that  round  one  star,  called  Aldebaran 
(No.  5,  Plate  I.),  there  must  bean  atmosphere  of  hydrogen, 
sodium,  magnesium,  calcium,  iron,  tellurium,  antimony,  bis- 
muth, and  mercury,  and  you  will  notice  that  the  last  four  of 
these  are  not  found  in  the  sun.  In  the  light  of  the  star 
Betelgeux,  in  the  constellation  Orion,  and  in  another  star, 
called  /3  Pegasi,  no  hydrogen  is  found,  but  it  is  found  in  all 
the  other  stars,  together  with  many  other  substances.  In 
some  of  the  stars  there  are  besides,  lines  which  are  not  found 
by  the  burning  gas  of  any  known  substances  on  our  earth. 

Dr.  Huggins  proves  that  some  Nebulae  are  Gaseous, 
1864. — And  now  we  come  to  a  very  interesting  experiment. 
You  will  remember  that  astronomers  doubted  Sir  W. 
Herschel  when  he  suggested  (p.  275)  that  some  of  the 
nebulae  are  not  made  of  tiny  stars,  but  of  gas  which  is 
forming  into  stars.  In  1864  Dr.  Huggins  began  to  examine 
these  nebulae  with  the  spectroscope,  and  he  found  that  they 
did  not  give  a  band  of  colour  with  dark  lines  upon  it  as  the 
stars  do,  but  a  feiu  faint  lines  on  a  dark  ground^  exactly  as 


328  NINETEENTH  CENTURY.  pt.  hi. 

gases  do  which  we  bum  here  on  earth.  If  you  compare  the 
spectrum  of  sodium  (No.  3),  or  of  hydrogen  (No.  4),  with  the 
nebula  spectrum  (N0.6),  you  will  see  at  once  that  the  nebula 
spectrum  is  made  by  a  gas,  and  so  the  truth  of  Sir  W. 
Herschel's  idea  was  proved,  and  there  can  be  now  no  doubt 
that  some  of  the  nebulae  are  composed  of  gaseous  matter ; 
chiefly,  so  far  as  we  can  learn,  of  nitrogen  and  hydrogen. 

Mr.  Alexander  Herschel  examines  the  Spectrum  of 
Falling  Stars. — I  have  said  that  it  was  difficult  to  examine 
the  spectrum  of  the  stars  and  nebulae,  but  something  which 
to  an  ordinary  observer  seems  still  more  wonderful  has  been 
lately  done.  Mr.  Alexander  Herschel  has  actually  caught  the 
light  oi  falling  stars  in  the  spectroscope,  and  in  this  way  has 
discovered  that  some  of  them  give  a  continuous  spectrum, 
showing  that  they  are  solid  bodies,  while  others  give  a  gas 
spectrum,  on  which  are  the  bright  lines  of  potassium,  sulphur, 
and  phosphorus,  but  chiefly  of  sodium. 

Such  wonderful  facts  as  thes.e  about  far-distant  suns  and 
sun-matter,  we  have  learnt,  and  are  still  learning  by  means 
of  spectrum  analysis.  The  whole  study  was  only  begun 
fifty  years  ago,  and  it  is  in  the  works  of  living  men  that 
you  must  look  for  the  details  of  its  history.  But  though 
many  eminent  names  are  connected  with  it,  those  of  Fraun- 
hofer  and  Kirchhoff  should  always  be  remembered  as  the 
chief  founders  of  the  science. 


Chief  Works  consulted.  — Roscoe's    *  Spectrum   Analysis  ; '    '  Edin- 
burgh Review,'  vol.  cxvi.  ;  *  Philosophical  Magazine,'  i860;  Proctor, 

•  The  Sun  ; '  Tyndall's  *  Lectures  on  Light ; '  *  Half-hours  with  Modern 
Scientists;'  Kirchhoff's   'Researches  on  the  Solar  Spectrum,'   1862; 

*  Encyclopaedia  Britannica, '  art.  *  Optics  ; '  Ganot's  '  Physics  ; '  Wol- 
laston,  *  On  Dispersion  ' — *  Phil.  Trans.'  1802;  Lockyer,  '  The  Spec- 
troscope.' 


cii.  XXXIV.  HEAT.  329 


CHAPTER  XXXIV. 

SCIENCE    OF   THE    NINETEENH    CENTURY    (CONTINUED). 

Early  Theories  about  Heat— Count  Rumford  shows  that  Heat  can  be 
produced  by  Friction — He  makes  Water  boil  by  boring  a  Cannon — 
Davy  makes  two  pieces  of  Ice  melt  by  Friction — His  conclusion 
about  Heat  —How  *  Latent  Heat '  is  explained  on  the  theory  that 
Heat  is  a  kind  of  Motion — Dr.  Mayer  suggests  the  Determination  of 
the  Mechanical  Equivalent  of  Heat — Dr.  Joule's  Experiments  on 
the  conversion  of  Motion  into  Heat — Dr.  Him's  Experiments  on  the 
conversion  of  Heat  into  Motion — Proof  of  the  Indestructibility  of 
Force,  and  Conservation  of  Energy'. 

Early  Theories  about  Heat.— From  Light  we  will  now 
pass  on  to  Heat,  and  in  this  chapter  I  hope  to  show  you  how 
the  philosophers  of  this  century  have  discovered  what  heat  is. 
The  subject  in  itself  is  so  vast  that  a  mere  sketch  of  all  the 
men  who  have  worked  at  it  and  their  chief  experiments 
would  fill  a  volume  of  this  size,  and  you  must  clearly  under- 
stand that  we  can  only  select  those  examples  which  will  best 
enable  you  to  comprehend  the  nature  of  heat,  and  how  it 
has  been  determined. 

Have  you  ever  asked  yourself  what  heat  is,  or  why 
the  mercury  in  a  thermometer  rises  when  it  is  put  into 
hot  water?  The  old  philosophers  considered  heat  to  be 
a  fluid,  which  passed  out  of  substances  when  they  were 
too  full  of  it,  and  which,  entering  the  mercury  of  the  ther- 
mometer, swelled  it  out  and  made  it  rise.  This  was  the 
general  idea  about  heat  up  to  the  end  of  the  eighteenth 


330  NINETEENTH  CENTURY.  pt.  in. 

century,  although  Lord  Bacon,  more  than  two  hundred 
years  before,  had  suggested  that  it  was  not  a  fluid  but  a 
movement,  and  the  philosopher  Locke,  in  the  seventeenth 
century,  and  Laplace  in  1780,  gave  the  same  explanation. 

Still  most  scientific  men  looked  upon  heat  as  a  fluid, 
which  they  called  caloric,  until,  in  the  year  1798,  Count  Rum- 
ford  first  showed  by  experiment  that  it  is  probably  a  kind  of 
motion.  In  following  strict  chronological  order,  this  dis- 
covery ought  to  have  been  mentioned  at  the  end  of  the 
eighteenth  century,  but  it  belongs  so  intimately  to  the  modern 
theory  that  it  comes  more  naturally  in  this  place. 

Count  Rumford  shows  that  Heat  can  be  produced  by 
Friction,  1798. — Benjamin  Thompson,  afterwards  Count 
Rumford,  was  born  in  the  United  States  in  1753.  He 
spent  his  early  life  fighting  in  the  English  army  against  the 
Americans,  in  the  War  of  Independence,  and  afterwards 
settled  at  Munich,  and  became  aide-de-camp  to  the  Elector 
of  Bavaria.  In  1798  he  came  over  to  England,  where  he 
was  one  of  the  founders  of  our  Royal  Institution,  and  finally 
he  died  in  Paris  in  1844. 

Rumford's  inquiries  into  the  nature  of  heat  began  in 
rather  a  curious  way.  He  was  very  anxious  to  make  the 
poorer  people  in  Bavaria  happier  and  more  prosperous,  and 
to  accomplish  this  he  persuaded  the  Elector  of  Bavaria  in 
1790,  to  forbid  anyone  to  beg  in  the  streets.  Those  who 
could  not  find  work  for  themselves  were  taken  up  and  kept 
in  a  kind  of  workhouse,  where  they  were  given  good  food 
and  clothing,  but  were  forced  to  work  to  pay  for  their  own 
support.  When  this  law  was  first  passed,  there  were  no 
less  than  2,500  beggars  to  be  provided  for,  and  Rumford 
was  obliged  to  calculate  very  closely  how  he  could  find 
food  and   clothing,  heat   and   light,  for  the   least  money. 


CH.  XXXI V.  COUNT  RUMFORD.  331 

Accordingly  he  studied  how  fire-places  could  best  be  built 
to  prevent  coal  being  wasted,  and  invented  a  lamp  which 
gave  a  brilliant  light,  without  burning  so  much  oil  as  other 
lamps  did.  He  even  went  so  far  as  to  make  a  complete 
set  of  experiments  on  different  clothing  materials,  in  order 
to  see  which  kept  in  the  most  heat.  It  was  in  this  way, 
and  especially  in  using  steam  for  warming  and  cooking, 
that  he  first  began  to  study  the  properties  of  heat,  and  he 
became  much  interested  in  the  different  ways  in  which  it 
may  be  produced. 

It  happened  one  day,  when  he  was  boring  a  cannon  in 
one  of  the  military  workshops  of  Munich,  that  he  noticed 
with  surprise  the  great  heat  produced  by  the  grinding  of  the 
borer  against  the  gun.  You  can  easily  make  a  similar  ex- 
periment by  boring  a  hole  quickly  with  a  gimlet  in  a  piece 
of  hard  wood,  and  on  withdrawing  the  gimlet  you  will  find 
that  it  is  hot  enough  to  burn  your  hand.  Rumford  examined 
carefully  the  gun  and  the  chips  which  fell  from  it,  and  found 
that  they  were  both  hotter  than  boiling  water. 

This  led  him  to  consider  how  it  could  possibly  happen, 
if  heat  were  a  fluid,  that  the  mere  rubbing  of  two  metals  to- 
gether should  produce  it ;  and  he  tried  many  experiments  to 
find  out  whether  the  gun,  the  chips,  or  the  borer  had  lost 
anything  in  consequence  of  having  given  out  heat.  But  he 
could  not  discover  that  they  were  changed  in  any  way ;  and 
moreover,  he  found  that  by  going  on  boring  he  could  make 
them  give  out  heat  as  long  as  he  liked,  whereas  if  he 
had  been  drawing  a  fluid  out  of  the  metals  it  seemed  to 
him  that  it  ought  to  come  to  an  end  sooner  or  later. 
Then  he  considered  whether  the  heat  could  come  out  of 
the  air,  and  to  avoid  this  he  repeated  the  experiment 
under  water,  but  still  the  metals  grew  hot,  and  even  made 


332  NINETEENTH  CENTURY.  pt.  hi. 

the  water  warm,  so  it  was  clear  they  had  not  drawn  any 
heat  from  that  fluid. 

He  now  began  to  suspect  that  Bacon  and  Locke  might 
be  right,  and  that  the  rubbing  together  of  the  two  metals 
might  set  their  particles  vibrating  in  some  peculiar  way  so 
as  to  cause  what  we  call  heat.  If  this  were  so,  then  by  great 
friction  he  ought  to  be  able  to  produce  any  amount  of  heat, 
and  to  prove  this  he  tried  the  following  experiment. 

He  took  a  large  piece  of  solid  brass  the  shape  of  a  can- 
non, and  partly  scooped  out  at  one  end.  Into  this  he  fitted 
a  blunt  steel  borer,  which  pressed  down  upon  the  brass  with 
a  weight  of  ten  thousand  pounds.  Then  he  plunged  the 
whole  into  a  box  holding  about  a  gallon  of  water,  into  which 
he  put  a  thermometer,  and  fastening  two  horses  by  proper 
machinery  to  the  brass  cylinder  he  made  them  turn  it  round 
and  round  thirty-two  times  in  a  minute,  so  that  the  borer 
worked  its  way  violently  into  the  brass.  Now  notice  what 
happened  :  When  he  began  the  water  was  at  60°  F.,  but 
it  soon  grew  warm  with  the  heat  caused  by  the  friction 
of  the  borer  against  the  brass.  In  one  hour  it  had  risen  47° 
up  to  107°  Fahr. ;  in  two  hours  it  was  at  178°,  and  at  the 
end  of  two  hours  and  a  half  //  actually  boiled. 

'  It  would  be  difficult,'  writes  Rumford,  ^  to  describe  the 
surprise  and  astonishment  of  the  bystanders  on  seeing  so 
large  a  quantity  of  water  heated  and  actually  made  to  boil 
without  any  fire,'  and  he  adds  that  he  himself  was  as  delighted 
as  a  child  at  the  success  of  the  experiment  j  and  we  can 
scarcely  wonder,  for  he  had  proved  the  grand  fact  that 
^notion  can  be  turned  into  heat! 

Rumford  afterwards  calculated  that  the  friction  caused 
by  one  horse  pulling  round  the  cylinder  against  the  borer 


CH.  xxxiv.  SIR  HUMPHREY  DAVY.  333 

was  sufficient  to  raise  26  lbs.   of  ice-cold  water  up  to  the 
boiling-point  in  two  hours  and  a  half. 

Davy  makes  Two  Pieces  of  Ice  melt  by  Friction  in 
a  Vacuum,  1799. — Only  a  few  months  after  Rumford  had 
made  the  discovery  that  heat  can  be  produced  by  friction, 
Sir  Humphry  Davy,  whose  history  as  a  chemist  you  will 
read  in  chapter  xxxvi.,  proved  the  same  thing  by  a  different 
experiment.  He  took  two  pieces  of  ice,  and  by  rubbing 
them  together  made  them  melt  without  any  warmth  being 
brought  near  them.  In  this  case,  as  he  said,  no  one  could 
think  that  the  heat  came  out  of  the  ice,  for  ice  holds  less 
heat  than,  water  ;  and  in  order  to  be  quite  sure  that  it  did 
not  come  out  of  the  air,  he  made  a  second  experiment  He 
took  a  small  piece  of  ice  and  put  it  in  a  machine  under  an 
air-pump,  by  means  of  which  he  drew  out  all  the  air ;  then 
he  set  his  machine  to  work  so  that  it  rubbed  against  the  ice, 
and  in  this  way  he  melted  the  whole  lump,  without  any  air 
being  present. 

Heat  a  Vibration. — From  these  experiments  Davy  came 
to  the  conclusion  'that  heat  is  a  peculiar  motion,  probably  a 
vibration  of  the  corpuscles  (that  is  the  little  particles)  of 
bodies,  tending  to  separate  them.'  Thus  for  example,  when 
you  put  a  saucepan  full  of  water  on  the  fire,  the  quivering 
motion  which  is  going  on  in  coals  as  they  burn  passes  into 
the  iron  of  the  saucepan,  and  through  it  to  the  water.  Im- 
mediately all  the  little  particles  of  which  the  water  is  com- 
posed are  pushed  asunder  as  if  they  were  trying  to  get  away 
from  each  other  ;  but  as  they  are  still  held  together  by  the 
force  of  attraction,  they  vibrate  to  and  fro,  struggling  more 
and  more  to  get  free,  and  it  is  this  motion  which  causes  in 
us  the  feeling  of  heat  when  we  come  in  contact  with  it. 
Then,  if  a  thermometer  be  placed  in  the  water,  the  vibration 


334  NINETEENTH  CENTUR  V.  .        pt.  hi. 

passes  on  through  the  glass  of  the  tube  into  the  mercury,  and 
the  particles  of  mercury  are  also  set  in  motion,  and  so  the 
mercury  swells  and  rises  in  the  tube. 

The  cause  of  Latent  Heat  explained. — And  now,  if 
you  will  look  back  for  a  moment  to  chapter  xxviii.,  and 
read  again  about  the  '  latent  heat '  which  puzzled  Dr.  Black 
so  much,  you  will  see  how  beautifully  it  can  be  explained 
by  this  theory  that  heat  is  a  kind  of  motion.  You  will 
remember  that,  however  much  heat  he  put  under  a  piece 
of  ice  he  found  that  the  temperature  of  the  water  would 
not  increase  above  o°  Cent,  so  long  as  a  morsel  of  ice 
remained  unmeltedj  and  again,  that  boiling  water  never 
grew  hotter  than  ioo°  Cent,  while  it  was  being  turned  into 
steam.  Now  if  we  look  upon  heat  as  a  vibration,  we  can 
understand  that  the  motion  which  is  sent  into  ice  from  the 
fire  below,  will  all  be  employed  in  overcoming  the  force  of 
attraction  and  separating  the  particles  of  ice  so  as  to  turn 
the  solid  into  a  fluid,  and  it  will  only  be  when  the  last 
particles  are  free  that  there  will  be  any  movement  to  spare 
so  as  to  produce  the  quivering  motion  of  heat.  Then  if 
you  go  on  heating  the  water  still  more,  the  struggling  move- 
ment will  continue  between  the  force  of  attraction  and  the 
force  of  motion,  and  so  the  water  will  grow  hotter  and  hotter, 
till  at  last  at  ioo°  Cent,  the  force  of  motion  wins  the  battle, 
and  the  little  particles  fly  asunder  and  float  away  as  steam  ; 
and  from  that  moment  all  the  extra  movement  is  employed 
in  forcing  asunder  particle  from  particle,  till  all  the  water 
has  passed  away  in  vapour. 

It  was  for  this  reason  that  Watt  had  to  use  so  much 
more  cold  water  to  cool  down  steam  of  ioo°  Cent,  than 
to  cool  down  water  of  ioo°  Cent. ;  for  in  cooling  down 
steam  he  had  not  only  to  get  rid  of  the  quivering  motion 


CH.  XXXIV.     DYNAMICAL    THEORY  OF  HEAT.  335 

of  heat,  but  of  all  the  extra  force  which  was  holding  the 
particles  asunder. 

Dr.  Joule's  Experimeiits  on  the  Conversion  of  Motion 
into  Heat,  1849. — It  had  now  been  shown  that  motion 
could  be  turned  into  heat,  and  Rumford  had  even  calculated 
roughly  how  much  heat  was  caused  by  a  certain  amount  of 
motion.  But  when  a  horse  walks  round  and  round  you  cannot 
measure  how  much  strength  he  gives  out,  and  in  order  to 
prove  that  motion  by  itself  can  produce  heat  we  must 
measure  exactly  how  much  motion  produces  a  definite 
quantity — say  1°  Fahr.  of  heat,  and  then  see  if  that  amount 
of  heat  can  be  turned  back  again  into  motion.  This  was 
done  by  Dr.  Joule,  of  Manchester,  a  celebrated  physicist, 
who  is  still  living. 

In  1839  a  Frenchman  named  M.  Seguin,  and  in  1842 
a  German  physician.  Dr.  Mayer,  of  Heilbronn,  both  sug- 
gested that  by  careful  experiments  it  might  be  found  out 
how  much  work  must  be  done  to  produce  a  certain  quantity 
of  heat,  and  Dr.  Mayer  made  many  calculations  about  it.  In 
1843,  without  having  heard  of  Dr.  Mayer's  suggestion.  Dr. 
Joule  began  those  famous  experiments  which  have  formed 
the  foundation  of  the  dynamical  theory  of  heat,  or  the  theory 
of  heat  produced  by  motion,  and  he  completed  them  in  1849. 
A  description  of  one  of  his  experiments  -wall  explain  the 
results  he  obtained.  He  took  a  weight,  a.  Fig.  53,  which 
weighed  i  lb.  and  fastened  it  by  strings  to  the  roller,//  On 
to  the  wheel,  b,  of  this  roller  he  wound  another  string  which 
passed  round  the  roller  r,  and  this  roller  was  attached  to  a 
paddle  which  was  shut  into  the  box  of  water,  c.  He  next 
wound  up  the  string  on  the  roller  /  so  as  to  draw  up  the 
weight  A,  and  then  set  it  free.  Immediately  the  force  of 
gravity  drew  the  weight  down  to  the  ground,  and  in  doing  so 


336  NINETEENTH  CENTURY.  pt.  in. 

pulled  round  the  wheel  b,  and  consequently  the  roller  which 
turned  the  paddle  in  the  water.  When  the  weight  reached 
the  ground  he  took  out  the  little  pin,  /,  which  fastened  the 
paddle  to  the  roller,  so  that  he  could  wind  up  his  apparatus 
without  disturbing  the  water  and  begin  again. 

Now  observe  how  this  measured  the  motion  and  the 
heat.  Every  time  the  weight  fell,  it  turned  the  paddle,  and 
so,  by  agitating  the  water,  added  to  its  heat.  The  scale,  d, 
told  him  exactly  how  far  the  weight  fell,  while  the  thermo- 
meter, t,  in  the  box  told  him  how  much  hotter  the  water 
grew.  At  the  end  of  an  hour,  therefore,  he  had  only  to  see 
how  many  feet  his  pound- weight  had  fallen,  and  how 
many  degrees  of  Fahr.  the  heat  of  his  water  had  risen ; 
and  after  allowing  for  the  friction  of  his  machinery  and 
for  the  heat  lost  in  the  cooling  of  his  vessel,  both  of  which 
he  ascertained  by  careful  experiments,  he  could  tell  how 
much  motion  had  been  used  up  in  producing  the  heat.  In 
this  way  he  found  that  a  weight  of  i  lb.  would  have  to  fall 
']']2  feet  in  order  to  make  i  lb.  of  water  warmer  by  i°  Fahr. 

He  next  tried  the  same  experiment  with  oil  and  with 
mercury  instead  of  water,  and  also  measured  the  heat  pro- 
duced by  rubbing  together  two  plates  of  iron  ;  and  in  every 
case  he  found  that  a  certain  amount  of  work  gave  a  certain 
amount  of  heat  and  no  more.  For  example,  if  the  weight 
in  Fig.  53  fell  double  the  distance,  the  heat  of  the  water  was 
raised  two  degrees  instead  of  one,  while  if  it  fell  only  half  the 
distance,  or  386  feet,  the  water  was  only  raised  half  a  degree. 

In  this  way  Dr.  Joule  established  what  is  called  the 
mechanical  equivalent  of  heat,  namely  that  the  fall  of  a  pound 
weight  through  772  feet  equals  the  heating  of  a  pound  of 
water  1°  Fahr.  And  now  you  must  try  to  foim  a  clear  idea 
what  this  means,  and  how  it  proves  that  heat  is  altered 


CH.  XXXIV.     CONVERSION  OF  MOTION  INTO  HEAT.      337 

motion.  Looking  at  the  diagram,  try  to  picture  to  your- 
self what  would  be  taking  place  if  the  weight  was  able  to 
fall  the  whole  772  feet  without  stopping.  First,  a  man  must 
wind  up  the  weight,  and  in  doing  this  he  uses  force  to  over- 
come the  force  of  gravitation  which  is  pulling  the  weight 
down  to  the  earth  ;  so  that  the  machine  starts  with  a  certain 
stock  of  force  stored  up  in  the  weight,  and  its  amount  is 
called   772  foot-pounds  because  it  has  raised  a  weight  of 


Joule's  Experiment  on  the  Conversion  of  Motion  into  Heat  (Phil.  Trans). 

A,  Weight.  15,  Wheel  of  the  roller,  _/"_/  c,  Vessel  containing  water  and  the  paddle. 
D,  Scale  to  measure  the  distance  that  the  weight  falls,  e,  Paddle  contained  in 
the  vessel,  c.  ff.  Roller  turned  by  the  falling  weight,  r.  Roller  turning  the 
paddle,  p.  Pin  which  joins  the  roller  and  the  paddle,  t.  Thermometer  plunged 
in  the  vessel,  c. 

I  lb.  to  a  height  of  772  feet.  This  stock  of  force  philoso- 
phers cslX  potential  energy ^  or  possible  energy  which  may  be 
called  into  use  at  any  time.  When  the  man  sets  the  weight 
free,  it  begins  to  fall,  drawn  down  by  the  force  of  gravity, 
and  the  stock  of  energy  is  set  free.  What  becomes  of  it? 
It  passes  by  the  wheel  b  into  the  roller  r,  and,  turning  the 
paddle  in  the  box,  enters  the  water.  If  the  water  were  free, 
16 


338  NINETEENTH  CENTURY.  pt.  iii. 

it  would  pass  on  into  the  air  and  we  should  lose  sight  of  it  ; 
but  the  water  is  shut  in  and  the  force  cannot  escape,  so 
now  it  employs  itself  in  dashing  to  and  fro  all  the  little 
particles  which  make  up  the  water,  and  producing  the  effect 
we  call  heat  j  and  as  it  produces  exactly  i°  Fahr.  of  heat 
by  the  time  the  i  lb.  weight  has  fallen  772  feet,  we  say 
that  772  foot-pounds  of  foi'ce  equals  1°  Fahr,  of  heat  You 
might  easily  prove  to  yourself  in  a  somewhat  unpleasant  way 
that  the  force  is  there ;  for  if  you  were  to  go  on  turning  the 
paddle  violently  for  many  hours,  and  there  were  no  means 
for  the  heat  to  escape,  the  motion  of  the  particles  would  be 
so  violent  against  the  sides  of  the  boiler  that  it  would  burst. 
Hirn's  Experiments  on  Heat  converted  into  Motion. 
— If  you  have  understood  this  explanation,  you  will  have 
some  idea  of  the  theory  that  heat  is  altered  motion  \  but  to 
complete  the  history  we  require  not  only  to  turn  work  into 
heat,  but  also  to  turn  heat  into  work.  This  had  already 
been  done  many  years  before  by  a  French  engineer,  M. 
Camot,  though  he  did  not  understand  its  real  significance, 
but  it  has  now  been  most  beautifully  proved  by  a  long 
series  of  experiments  made  by  M.  Hirn,  of  Colmar,  in 
Alsace.  What  M.  Hirn  practically  did  was  to  find  out  how 
much  heat  can  be  obtained  from  a  ton  of  coals,  and  then  to 
find  out  how  much  work  v/as  performed  in  an  engine  by 
that  amount  of  heat.  This  was  by  no  means  a  simple  task, 
for  much  heat  is  lost  in  various  ways  in  passing  through  the 
engine ;  and  even  when  he  thought  he  had  allowed  for  all 
this,  it  was  found  that  some  of  the  steam  had  turned  back 
into  water  on  its  way,  and  thus  used  up  some  of  the  heat. 
At  last,  however,  when  all  was  carefully  measured  and  calcu- 
lated, he  found  that^r  every  pound  of  water  heated  1°  Fahr.^ 
enough  work  had  been  done  to  raise  a  weight  of  i  lb.  to  a 


CH.  XXXI '/.         CONSERVATION  OF  ENERGY,  339 

height  of  1"]  2  feet.  This,  you  will  notice,  was  exactly  the  con- 
verse of  Joule's  experiment,  and  proved  that  exactly  as  much 
motion  is  produced  by  means  of  confined  heat  as  there  is 
heat  produced  by  means  of  checked  motion. 

Conservation  of  Energy. — And  thus  we  arrive  at  one 
of  the  grandest  discoveries  of  modern  science,  namely,  that 
the  whole  amount  of  enei'gy,  or  power  of  doing  work,  pos- 
sessed by  any  set  of  bodies,  remains  unaltered  whatever 
transformations  it  may  undergo.  It  may  exist  in  one  of 
two  forms — either  djs>  potential  or  stored-up  energy,  which  is 
unseen  by  us,  or  as  visible  enei'gy,  when  it  is  actually  per- 
forming work  ;  but  while  it  changes  from  one  form  to  another 
its  amount  never  alters.  Thus  in  Joule's  experiment  the 
energy  stored  up  in  the  weight  which  had  been  pulled  up 
772  feet  was  gradually  transformed,  as  soon  as  the  weight 
was  released,  into  an  amount  of  heat  capable  of  raising  the 
temperature  of  a  pound  of  water  1°  Fahr.  ;  while  Him 
showed,  on  the  other  hand,  that  exactly  this  amount  of  heat 
can  be  turned  back  into  enough  energy  to  raise  a  weight 
to  the  height  of  772  feet  at  which  it  stood  before. 

The  potential  energy,  or  power  of-doing  work,  remained, 
therefore,  exactly  the  same  whether  it  was  stored  up  in  the 
weight  or  in  the  hot  water,  and  reproduced  exactly  the  same 
amount  of  visible  energy  or  actual  work.  And  even  though 
we  know  that  practically  some  energy  disappears  at  every 
part  of  a  machine  when  it  is  at  work,  yet  this  is  not  lost ;  for 
it  turns  into  heat  wherever  it  disappears  as  motion.  If  you 
grease  the  wheels  of  a  machine,  you  will  detect  this  heat 
beginning  to  do  work  again  by  turning  the  solid  grease  into 
a  liquid. 

By  whatever  means,  therefore,  heat  is  turned  into  motion, 
or  motion  into  heat,  the  energy  which  causes  them  both 


340  NINETEENTH  CENTURY.  pt.  ill 

remains  the  same,  and  this  is  one  out  of  many  proofs  that 
force  cannot  be  destroyed,  but  is  only  lost  in  one  form  to  re- 
appear in  another. 

Other  Experiments  on  Heat. — Although  the  experiments 
and  calculations  which  have  proved  heat  to  be  a  kind  of 
motion  are  some  of  the  most  interesting  which  have  been 
made  of  late  years,  yet  they  are  by  no  means  the  only  ones. 
In  1811  Sir  John  Leslie  carried  on  a  most  interesting  series 
of  observations  on  the  reflection  of  heat  j  and  the  Italian 
physicist  Melloni  has  traced  the  whole  passage  of  heat- 
rays  through  different  solid  bodies.  All  these  discoveries 
are  clearly  and  simply  described  in  Professor  TyndalFs 
work  on  'Heat,'  where  you  may  also  find  the  great  addi- 
tions that  he  has  himself  made  to  the  work  of  these  men. 

We  must  content  ourselves  here  with  remembering  that 
the  physicists  of  the  nineteenth  century  have  shown  that 
heat  is  'a  mode  of  motion,'  and  have  traced  it  through 
all  its  many  wanderings  both  in  earth,  air,  and  sky.  They 
have  even  followed  it  from  the  sun  down  to  our  earth, 
through  the  plant-world  into  the  beds  of  coal  which  are 
stored  up  in  our  rocks,  and  back  again,  when  this  coal  is 
burnt,  to  the  motion  which  carries  our  steam-engines  and 
steam-ships  across  the  world.  All  this  lies  before  you  to 
study  in  books  of  scien'ce,  but  now  we  must  pass  on  to 
new  discoveries  in  two  remarkable  sciences,  namely,  elec- 
tricity and  magnetism,  which,  we  shall  find,  are  closely 
bound  up  with  heat  and  motion. 


Chief  Works  co7tsulted, — Rumford's  'Essays,'  vol.  ii.  —  'Friction  a 
Source  of  Heat,'  1798;  Davy's  'Works,'  vol.  ii. — 'Essay  on  Heat 
and  Light ; '  Joule's  '  Mechanical  Equivalent  of  Heat ' — '  Phil,  Trans.,' 
1850;  Mayer's  'Forces  of  Inorganic  Nature' — 'Phil.  Mag.,'  1843; 
Tyndall's  '  Heat  a  Mode  of  Motion  ; '  Watts's  '  Diet,  of  Chemistry,' 
art.    'Heat  ;'  Clerk-Maxwell's  'Theory  of  Heat.' 


cii.  XXXV.  OERSTED.  341 


CHAPTER  XXXV. 

SCIENCE   OF   THE   NINETEENTH   CENTURY   (CONTINUED). 

Oersted  discovers  the  effect  of  Electricity  upon  a  Magnet — Electro- 
magnetism — Experiments  by  Ampere  on  Magnetic  and  Electric 
Currents — Ampere's  Early  Life — Direction  of  the  North  Pole  of  the 
Magnet  depends  on  the  course  of  the  Electric  Currents — Magnetic 
Currents  set  up  between  two  Electric  Wires  —  Electro-magnets 
made  by  means  of  an  Electric  Current — Arago  magnetises  a  Steel 
Bar  with  an  ordinary  Electrical  Machine — Faraday  discovers  the 
Rotatory  Movement  of  Magnets  and  Electrified  Wires — Produces 
an  Electric  Current  by  meams  of  a  Magnet — Seebeck  discovers 
Thermo-electricity,  or  the  production  of  Electricity  by  Heat — 
Schwabe  discovers  Periodicity  of  the  Spots  on  the  Sun — Sabine  sug- 
gests a  connection  between  Sun-spots  and  Magnetic  Currents — This 
proved  in  1859  by  observations  of  Carrington  and  Hodgson — 
Electric  Telegraph —  Wheatstone  —  Cooke  —  Steinheil — Morse  — 
Bain. 

Oersted  discovers  the  Effect  of  Electricity  upon  a  Mag- 
net, 1820. — We  left  the  history  of  electricity  at  p.  264,  at 
the  point  where  Volta  had  shown  in  1800  that  two  diffe- 
rent metals  joined  by  a  wire  and  placed  in  acid  and  water 
will  set  up  two  currents  of  electricity  flowing  in  opposite 
directions  from  one  metal  to  the  other  along  the  wire,  and 
back  through  the  water.  Every  galvanic  battery^  that  is,  an 
apparatus  for  producing  electricity  by  chemical  action,  is 
made  on  this  principle.  You  will  hear  of  Grove's  battery, 
Bunsen's  battery,  Daniell's  battery,  and  many  others,  all  of 
which  have  been  invented  in  the  present  century ;  but  all 


342  NINETEENTH  CENTURY.  rx.  in. 

these  are  only  different  and  more  perfect  methods  of  carry- 
ing out  Volta's  discovery.  The  next  great  step  in  the  study 
of  electricity  was  made  by  Oersted,  Professor  of  Physics  at 
Copenhagen,  in  1820,  twenty  years  after  the  invention  of 
the  voltaic  pile. 

Hans  Christian  Oersted  was  born  in  1777,  and  died  in 
185 1 ;  he  was  a  very  eminent  man,  and  wrote  many  works  in 
Latin  upon  chemistry  and  magnetism,  but  the  one  discovery 
which  has  made  him  famous  was  that  of  electro-magnetism. 
We  have  seen  (p.  53)  that  the  invention  of-  the  mariner's 
compass  in  the  fifteenth  century  arose  from  Flavio  Oioja 
noting  that  a  needle  which  has  been  rubbed  along  a  piece  of 
loadstone  always  points  north  and  south.  But  why  should 
the  needle  lie  in  this  direction  ?  What  force  m^akes  it  turn 
round  when  you  leave  it  free  after  placing  it  another  way  ? 
Ever  since  the  fifteenth  century  people  had  asked  this  ques- 
tion, and  when  Volta  and  Franklin  showed  that  electrical 
currents  are  constantly  passing  to  and  fro  in  our  atmosphere, 
scientific  men  began  to  consider  whether  it  might  not  be 
some  force  like  electricity  which  acted  upon  the  magnet ;  es- 
pecially as  it  had  been  observed  that  when  a  ship  was  struck 
by  lightning,  the  needle  of  the  mariner's  compass  was  some- 
times thrown  quite  out  of  its  right  position. 

Still  nothing  was  really  known  until  the  year  18 19.  In 
that  year,  when  Professor  Oersted  was  one  day  making  some 
galvanic  experiments  at  a  lecture,  it  happened  that  a  magnetic 
needle  poised  upon  a  point  (as  in  Fig.  54)  was  standing 
near  the  wire  along  which  an  electric  current  was  passing. 
All  at  once,  when  the  current  was  very  strong,  the  needle 
became  excited  and  began  to  turn  round  upon  the  point. 
Oersted  and  his  assistants  were  much  surprised  at  this,  and 
the  consequence  was  that  for  several  months  Oersted  made 


CH.  XXXV. 


ELECTRO  MA  GNETISM. 


343 


a  series  of  experiments  by  which  he  proved  that  an  electric 
current  passing  near  a  magnetic  needle  will  always  make  it 
turn  round  so  as  to  lie  across  the  path  of  the  ctcrretit. 

For  example,  if  the  bar  of  copper  wire  a  b,  supported  on 
the  glass  rods  <f,  e,  be  so  placed  that  the  end  b  points  to  the 
north  and  a  to  the  south,  then  the  magnetic  needle  c  will 
lie  exactly  in  a  line  with  the  bar,  because  a  magnet  always 
points  north  and  south.  But  if  the  two  ends  of  the  copper 
rod  a^  bf  are  fixed  to  the  wires  of  a  voltaic  battery  d,  Fig.  54, 
so  that  an  electric  current  runs  along  the  rod  from  a  to  b, 
then  the  north  end  of  the  needle  will  begin  to  move  away 
from  the  north  towards  the  west,  that  is  towards  the  left  side 

Fig.  54. 


Magnet  turned  by  an  Electric  Current. 

a  h.  Rod  of  copper  wire.    c\  Magnetic  needle,    d.  Voltaic  pile  (explained  p.  263). 
e  e,  Glass  supports  to  prevent  the  current  running  down  to  the  ground. 

of  the  current  j  and  it  will  turn  more  and  more  as  the  current 
grows  stronger,  till  it  lies  right  across  it,  pointing  direct  east 
and  west. 

This  was  a  very  grand  fact,  and  it  has  become  the  begin- 
ning of  a  new  science  called  electro-magnetism,  for  it  shows 
that  electricity  and  magnetism  act  upon  each  other  in  some 
peculiar  way.  Oersted  did  not  publish  an  account  of  his 
experiments  until  1820,  and  then  the  whole  of  Europe  rang 
with  the  news  of  the  discovery. 

Ampere,  1775-1864.— One  of  the  first  men  who  heard 


344  NINETEENTH  CENTURY.  pt.  ill. 

of  it  was  Ampere,  one  of  the  professors  at  the  Ecole  Poly- 
technique  in  Paris.  We  must  pause  a  moment  to  learn 
something  of  the  early  history  of  this  man,  for  it  is  very  inte- 
resting. Andre  Ampere  was  born  at  Lyons  in  1775.  When 
he  was  quite  a  little  boy  he  delighted  in  arithmetic,  and 
used  to  do  long  sums  for  his  amusement  by  means  of  little 
pebbles  which  he  arranged  in  groups.  Once  when  he  had  a 
severe  illness  his  mother  took  the  stones  away,  but,  having 
left  him  alone  one  day  for  a  little  time,  she  found  on  her  re- 
turn that  he  had  broken  his  biscuit  into  little  bits  and  was 
using  them  to  work  with  instead  of  his  lost  pebbles.  As  he 
grew  older  his  father  began  to  teach  him  Latin,  but  the  boy 
disliked  it  so  much  that  it  was  given  up,  and  he  devoted  all 
his  time  to  Algebra  and  Euclid. 

One  day  he  persuaded  his  father  to  take  him  to  his  friend, 
the  Abbe  Daburon,  to  borrow  the  ^vritings  of  Euler  and 
Bernouilli,  two  great  mathematicians.  The  Abbe  stared  at 
this  little  boy,  only  twelve  years  old,  asking  for  books  which 
very  few  men  could  understand.  '  Do  you  know,  my  little 
fellow,'  said  he,  '  that  these  works  are  Avritten  in  Latin,  and 
that  the  differential  calculus  is  used  in  them  ? '  Andre's 
countenance  fell  for  a  moment,  for  he  knew  neither  of  these 
things.  But  he  soon  brightened  up  again.  *  Never  mind,' 
he  replied,  *  I  can  learn  them,^  and  he  set  to  work  that  very 
day  to  learn  Latin  with  his  father,  and  the  differential  calculus 
with  the  Abbe,  and  in  a  few  months  was  able  to  come  back 
for  the  books  he  coveted. 

Before  he  was  eighteen  he  had  not  only  read  the  whole 
of  Laplace's  'Mecanique  Celeste,'  but  had  even  worked 
out  all  the  complicated  problems  in  it.  He  had,  however, 
overtaxed  his  brain,  and  when  his  father  was  killed  in  the 
terrible  French  Revolution  of  1793,  the  grief  broke  down  his 


CH.   XXXV. 


AMPERE. 


345 


intellect.  For  a  whole  year  he  was  almost  an  idiot,  and  it 
was  a  long  time  before  he  could  take  up  his  mathematical 
studies  again.  When  he  did,  it  was  with  his  old  love  of 
work,  and  he  became  a  teacher  first  at  Lyons,  and  afterwards 
in  Paris. 

Ampere's  Experiments  upon  Magnetic  and  Electric 
Currents,  1820. — This  was  the  man  who  heard  of  Oersted's 
discovery  in  1820.  You  can  imagine  the  delight  with  which 
he  seized  upon  the  new  idea.  He  worked  at  it  incessantly,  as 
he  had  done  with  his  pebbles  when  a  boy,  and  before  a  week 
was  over  he  had  proved  several  new  facts  about  electro- 
magnetism.  He  found  that  it  was  quite  true  as  Oersted  had 
said,  that  the  magnet  always  lies  across  the  electric  current; 
but  he  showed  that  the  north  pole  of  the  magnet  turns 
different  ways,    according   to   the    direction  in  which   the 


Fig.  55. 


Fig.  56. 


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Diagrams  showing  the  direction  of  a  Magnet  acted  upon  by  Electric  Currents. 
a,  b,  c,  d.  Direction  of  current. 

current  flows.  Thus,  if  the  current  ^  flows  from  sotctk  to  north 
above  the  magnet,  in  the  direction  a  b,  Fig.  55,  then  the 
north  pole  of  the  magnet  turns  towards  the  west ;  but  if  it 
runs  from  north  to  south  above  the  magnet,  in  the  direction 


'  You  must  bear  in  mind  that  there  are  always  two  cuiTents,  one 
from  the  negative  and  the  other  from  the  positive  pole  of  the  battery  ; 
but  to  avoid  confusion  the  positive  current  is  always  spoken  of  as  t?ie 
current. 


346  NINETEENTH  CENTURY,  pt.  hi. 

a  b,  Fig.  56,  then  the  north  pole  turns  towards  the  east. 
Again,  if  it  runs  from  north  to  south  below  the  magnet,  in 
the  direction  c  d,  Fig.  55,  the  magnet  will  again  turn  to  the 
west ;  while  lastly,  if  it  runs  from  south  to  north  below  the 
magnet,  c  d,  Fig.  56,  the  north  pole  turns  again  to  the  east. 
In  order  to  remember  these  different  directions  easily, 
Ampere  gave  something  like  the  following  rule.  If  a  man 
will  imagine  himself  to  be  standing  so  that  the  positive  current 
would  come  out  of  his  mouth  and  return  by  his  feet ^  the  north 
pole  of  the  magnet  will  always  be  on  his  left-hand  side.  If 
you  are  fond  of  standing  on  your  head,  and  will  try  the 
positions  in  Figs.  55  and  56,  you  will  see  that  this  is  so— the 
north  pole  of  the  magnet  will  always  be  towards  your  left 
hand. 

Magnetic  Currents  set  up  between  two  Electric  Wires. — 
The  next  discovery  which  Ampere  made  was  a  very  impor- 
tant one.  It  was  already  well  known  that  two  magnetic 
needles  will  either  attract  or  repel  each  other  according  to 
the  position  of  their  poles.  Thus,  if  the  north  pole  of  one 
needle  is  held  towards  the  south  pole  of  another,  they  are 
attracted  strongly  together,  but  if  the  two  north  poles  are 
brought  near  together,  the  movable  needle  is  repelled.  Now 
Ampere  argued  that  if  an  electric  current  always  causes  a 
magnetic  current  across  itself,  then  two  electric  wires  side  by 
side  will  have  magnetic  currents  running  across  them,and  they 
ought  to  attract  or  repel  each  other  as  if  real  magnets  were 
lying  between  them.  And  this  he  proved  to  be  true.  He 
put  two  wires  side  by  side  in  such  a  position  that  they  could 
move  freely,  and  when  he  sent  an  electric  current  in  the 
same  direction  through  each  of  them  they  moved  towards 
each  other-;  while,  if  he  sent  the  currents  one  way  through 
one  wire  and   the  other  way  through  the  other,  they  drew 


CH.  XXXV.      EXPERIMENTS  IN  MAGNETISM.  347 

apart ;  exactly  in  the  same  way  as  magnets  attract  or  repel 
each  other,  according  to  the  direction  in  which  they  lie. 

This  may  be  difficult  to  understand  without  more  expla- 
nation, but  you  can  remember  that  Ampere  proved  that  eke- 
tric*currents  J>roduce  magnetic  cui'rents  at  right  angles  to  them- 
selves in  the  air,  without  needing  any  bar  of  steel  to  help  them. 

Electro-magnets  made  by  means  of  an  Electric  Current. 
— It  now  occurred  to  Ampere  that  if  electric  currents  give 
rise  to  magnetic  currents  he  ought  to  be  able  to  magnetise  a 
steel  bar  by  passing  an  electric  current  round  it.  So  he 
wound  a  copper  wire  (covered  with  silk  to  prevent  the 
electricity  running  into  the  iron)  round  a  steel  bar,  and, 
fastening  the  two  ends  of  wire  to  a  voltaic  battery,  he  passed 
a  current  through  it  (see  Fig.  57).  After  a  short  time  he  took 

Fig.  57. 


^is^^^s^iet^K^Ki^^c^^i^^ 


Coll  of  Electrified  Copper  Wire  turning  a  Steel  Bar  into  a  Magnet. 

the  bar  out  and  found  it  was  a  perfect  bar  magnet,  which 
would  attract  iron.  The  current  of  electricity,  in  passing 
along,  had  magnetised  the  steel  just  as  if  it  had  been 
rubbed  on  a  loadstone. 

Steel  is  very  close  and  hard,  and  when  he  used  a  steel 
bar  the  magnetism  remained  after  it  was  taken  out  of  the 
electric  wire,  but  if  he  used  a  piece  of  ordinary  soft  iron  the 
magnetism  passed  away  when  the  current  ceased.  He  called 
these  magnetised  bars  electro-magnets,  because  they  are  made 
by  electricity.  You  can  easily  make  them  for  yourself,  and 
you  will  find  that  an  iron  rod  will  hold  up  needles,  nails,  or 
even  keys  as  long  as  the  current  is  passing,  but  they  will  all 
fall  off  as  soon  as  it  stops,  showing  that  it  is  the  electric 
current  which  causes  the  iron  to  act  as  a  magnet. 


348  NINETEENTH  CENTUR  K  pt.  iil 

Professor  Arago,  whom  we  mentioned  before  (p.  311)  as 
making  experiments  on  light,  succeeded  in  magnetising  a 
steel  bar  with  currents  from  an  ordinary  electrical  machine, 
that  is,  a  glass  cylinder  rubbed  against  silk,  instead  of  using 
a  battery.  * 

Michael  Faraday,  1791-1867. — We  must  now  travel 
back  to  England,  where  one  of  our  greatest  philosophers  was 
watching  these  new  discoveries  with  intense  interest.  Michael 
Faraday,  the  son  of  a  poor  journeyman  blacksmith,  was  born 
at  Newington  Butts  in  1791.  When  he  was  thirteen  years 
old  he  went  as  errand  boy  to  a  bookseller  named  Mr. 
Rieban,  in  Blandford  Street,  Manchester  Square,  and  it  was 
there  that  the  books  fell  into  his  hands  which  first  awoke 
his  love  of  science.  Mrs.  Marcet's  '  Conversations  on 
Chemistry,'  Lyons's  '  Experiments  on  Electricity,'  and  other 
books  of  a  like  kind  made  the  lad  long  for  more  knowledge 
about  these  wonderful  sciences.  He  constructed  an  elec- 
trical machine,  and  spent  his  evenings  in  making  experi- 
ments, and  he  persuaded  his  brother  Robert  to  pay  a  few 
shillings  for  him  to  attend  some  lectures  given  by  a 'Mr. 
Tatum  on  Natural  Philosophy. 

But  one  of  the  first  great  pleasures  of  his  life  was  when 
a  customer  at  the  bookshop,  a  Mr.  Dance,  took  him  to  four 
lectures  at  the  Royal  Institution,  given  by  Sir  Humphry - 
Davy.  These  lectures  filled  him  with  an  intense  longing 
to  learn  more,  and  he  took  the  bold  step  of  writing  a  letter 
to  Davy,  enclosing  the  notes  which  he  had  made  of  the 
lectures,  and  asking  for  some  employment  connected  with 
science.  It  will  always  be  remembered  to  Davy's  honour 
that  he  did  not  throw  this  letter  aside,  but  wrote  a  kind 
reply,  telling  the  young  man  to  come  and  see  him,  and 
in  the  end  made  him  his  assistant  at  the  Royal  Institution 


CH.  XXXV.  FAI^ADAY. 


319 


in  Albemarle  Street,  \vhere  Faraday  afterwards  became  Pro- 
fessor of  Chemistry. 

It  is  impossible  in  a  short  sketch  to  give  you  any  idea  of 
the  simple  and  noble  nature  of  the  man  who  from  that  time 
for  more  than  fifty  years  laboured  at  science  in  the  Royal 
Institution.  It  is  not  yet  eight  years  since  he  died,  and  you 
may  talk  with  many  who  have  known  and  loved  him,  and 
if  you  wish  to  learn  the  story  of  his- life  you  must  read  it  in 
the  book  called  '  Michael  Faraday,'  written  by  Dr.  Gladstone. 
Even  of  his  experiments  we  can  only  mention  a  few,  for  these 
subjects  are  becoming  almost  too  deep  for  us ;  but  those 
which  we  must  now  consider  were  some  which  have  helped 
to  make  his  name  famous. 

Faraday  discovers  the  Mutual  Rotation  of  Magnets 
and  Electrified  Wires,  1821. — It  was  in  1821  that  Faraday 
began  to  repeat  for  himself  Ampere's  experiments  on  elec- 
tricity and  magnetism,  and  he  soon  saw  that  if  an  electric 
current  going  round  a  wire  gave  rise  to  magnetic  currents  at 
right  angles  to  it,  he  ought  to  be  able  to  make  an  electric 
wire  revolve  round  a  magnet,  and  a  magnet  round  an  elec- 
tric wire.  Accordingly,  he  took  two  cups  of  mercury,  a  b. 
Fig.  58,  p.  350,  and  drilling  a  hole  in  the  bottom  of  each,  he 
passed  the  wires  e^  e',  of  a  battery  up  into  them  j  then  he 
took  two  magnets  d,  d' ;  d  he  fastened  by  a  thin  thread  to 
the  battery  wire  in  the  cup  a,  so  that  it  floated  upright  in 
the  mercury,  and  the  top  of  it  could  move  round  easily  ;  the 
other  magnet,  d,  he  fixed  firmly  upright  in  the  cup  b.  He 
then  hung  the  copper  rod  c  above  the  cups,  so  that  the  end 
f,  which  was  fixed,  dipped  into  the  cup  A,  and  the  other 
end,  which  was  made  of  a  loose  moveable  wire,  f,  dipped 
into  the  cup  b.  Thus  in  a  the  magnet  was  free  to  move 
and  the  wire  was  fixed,  while  in  b  the  wire  was  free  to  move 


35^ 


NINETEENTH  CENTURY, 


PT.   III. 


and  the  magnet  was  fixed.  He  now  sent  a  current  through 
the  wires  e,  e',  and  immediately  in  the  cup  a  the  magnet  d 
began  to  move  round  the  fixed  wire^  while  in  b  the  wire/' 
moved  round  the  fixed  magnet,  d'.  In  this  way  he  proved 
that  magnetic  and  electric  currents  move  round  and  round  in 
circles  at  right  angles  to  each  other.     He  made  the  magnet  go 


Faraday's  Experiments  on  the  Rotation  of  a  Magnet  and  of  an  Electric  Wire 

(Brande). 

A  B,  Section  of  cups  of  mercury,  c.  Copper  rod.  The  current  coming  in  at  e  passes 
up  through  the  mercury  in  a,  and  along  the  rod  c  down  into  the  mercury  in  b, 
and  back  by  ^  to  the  battery.  On  its  way  it  causes  the  floating  magnet,  d,  to 
revolve  round  the  rod,  f,  and  the  loose  wire,  _/',  to  revolve  round  the  fixed 
magnet,  d!. 

a  great  way  round  the  circle,  but  not  spin  quite  round  as 
the  wire  had  done.  Ampere,  however,  who  repeated  the 
experiment,  succeeded  in  making  the  magnet  spin  round  and 
round  like  the  hands  of  a  clock. 

Electric  Current  produced  by  means  of  a  Magnet.— 
Faraday's  mind  was  now  full  of  the  wonderful  effect  which 
electricity  and  magnetism  produce  on  each  other,  and  he 
began  to  consider  whether  it  might  not  be  possible  to  reverse 
Ampere's  second  experiment  (p.  347),  and  instead  of  making 
a  magnet  by  means  of  an  electric  current,  whether  he  might 
not  set  up  an  electric  current  by  means  of  a  magnet. 


CH.  XXXV. 


THE  INDUCTION  COIL. 


351 


To  try  this  he  wound  from  200  to  300  yards  of  wire 
round  a  hollow  cylinder  a,  Fig.  59,  and  carried  the  two 
ends  of  the  wire  to  a  little  instrument  b,  called  a  galvano- 
meter, which  was  invented  by  Ampere,  and  the  needle  of 
which  moves  directly  the  slightest  current  passes  through  it. 
He  then  took  a  powerful  bar  magnet,  c,  and  held  it  within  the 
cylinder.  The  moment  he  put  it  in,  the  needle  of  the  galvano- 
meter showed  that  an  electric  current  had  passed  through 


Fig.  59. 


Faraday's  Experiment  on  creating  an  Electric  Current  by  means  of  a  Magnet 

(Ganot). 

a.  Coil  of  wire  round  a  wooden  cylinder  connected  at  the  two  ends  with  b,  a  galvano- 
meter, the  needle  of  which  shows  directly  a  current  passes  through  the  wire ;  c,  a 
powerful  magnet. 

the  wire  in  one  direction,  and  the  moment  he  drew  it  out 
another  rush  of  electricity  occurred  in  the  other  direction, 
showing  that  the  magnet  had  set  up  an  electric  current  in  a 
coil  of  wire.  While  the  magnet  remained  in  the  cylinder 
there  was  no  current  \  it  was  only  at  the  moment  of  going  in 
and  coming  out  that  it  produced  the  effect.  By  a  more 
complicated  apparatus  Faraday  succeeded  in  making  these 
currents  strong  enough  to  produce  electric  sparks ;  and  it  is 


352  NINETEENTH  CENTUkY.  pt.  iir. 


on  this  principle  that  the  induciion-coil  is  made  which  is 
now  used  to  increase  the  power  of  the  electricity  coming 
from  an  electric  battery. 

Professor  Seebeck  discovers  Thermo-electricity,  or  the 
Production  of  Electricity  by  Heat. — The  fact  was  now 
clearly  established  that  electric  and  magnetic  currents  move 
at  right  angles  to  each  other,  and  this  gives  to  a  certain 
extent  the  answer  to  our  question.  Why  does  a  magnet 
turn  to  the  north?  Ampere  suggested  quite  early  in  the 
discussion,  that  if  an  electric  current  will  turn  metals  into 
magnets,  the  electric  currents  which  we  know  are  flowing 
from  east  to  west  round  our  globe,  may  turn  the  earth 
(which  is  full  of  metals)  into  a  great  magnet.  But  it  is 
also  true  that  exactly  the  opposite  effect  is  possible,  and  that 
the  magnetic  currents  may  be  started  ^by  some  other  cause 
and  may  set  up  the  electric  currents,  so  that  we  do  not 
really  know  which  gives  rise  to  the  other. 

An  interesting  discovery  was,  however,  made  in  1822 
by  Professor  Seebeck,  showing  a  possible  cause  of  the 
electric  currents  flowing  from  east  to  west.  He  wished  to 
try  whether  he  could  not  give  rise  to  a  current  of  electricity 
in  two  metals  by  merely  using  heat  instead  of  acid  and 
water.  For  this  purpose  he  took  a  half  ring  of  copper  and 
fastened  to  it  a  bar  of  a  metal  called  antimony,  so  that  the 
two  metals  had  the  form  of  a  stirrup,  and  inside  this  stirrup 
he  hung  a  magnetic  needle,  which  would  show  if  any 
current  passed  along  the  metals.  Then  he  heated  one  of 
the  corners  where  the  metals  joined,  and  immediately  the 
magnet  began  to  turn,  showing  that  an  electric  current  was 
passing  through  the  copper,  and  back  through  the  antimony. 
He  tried  this  with  many  other  metals,  and  in  every  case 
when  one  of  the  parts  where  they  joined  was  made  hotter 


CH.  XXXV.  SCHWABE  AND  SABINE.  353 

than  the  rest,  a  current  of  electricity  was  caused.  This  he 
called  thermo-etedricity^  or  electricity  caused  by  heat,  and  it 
gives  us  another  beautiful  instance  of  the  transformation  of 
energy.  We  saw  in  chapter  xxxiv.  that  heat  is  altered  mo- 
tion and  motion  altered  heat ;  since  then  we  have  learnt  that 
electricity  produces  magnetism  and  magnetism  electricity, 
and  now  we  have  heat  in  its  turn  causing  electricity,  while 
we  know  from  the  electric  spark  that  electricity  produces 
both  light  and  heat.  In  all  these  changes  we  see  additional 
proof  that  force  or  energy  cannot  be  destroyed,  but  only 
exhibits  itself  in  different  ways. 

But  to  return  to  the  magnet.  Seebeck's  experiment  sug- 
gests a  possible  answer  to  the  direction  of  the  magnetic 
needle  to  the  north.  Our  globe  is  composed  of  different 
metals  and  earths,  and  is  always  turning  round  from  west  to 
east,  so  that  one  part  after  another  comes  under  the  heat  of 
the  sun,  and  is  made  hotter  than  the  rest.  Therefore,  since 
heat  produces  electricity,  it  has  been  suggested  that  this  may 
cause  the  electric  currents  to  flow  round  from  east  to  west, 
as  they  did  through  the  metals  in  Seebeck's  stirrup,  thus 
inducing  magnetic  currents  to  flow  round  from  north  to 
south.  Our  knowledge  on  this  subject  is,  however,  very 
imperfect,  and  the  observations  of  which  we  shall  next  speak 
seem  to  point  to  some  closer  connection  between  the  sun 
itself  and  magnetic  currents. 

Periodicity  of  the  Spots  on  the  Sun,  and  their  Effect  on 
the  Earth's  Magnetism,  discovered  by  Schwabe  and  Sabine, 
1825-1859. — It  was  mentioned  at  p.  92  that  Galileo  and 
other  astronomers  of  the  seventeenth  century  first  observed 
that  from  time  to  time  dark  spots  appear  on  the  face  of  the 
sun.  These  spots  were  much  studied  by  the  astronomers 
who  came  after  Galileo;  but  Sir  William  Herschel  was  the 


354  NINETEENTH  CENTURY.  pt.  hi. 

first  to  suggest  in  1793  that  they  are  caused  by  the  opening 
of  bright  luminous  clouds  which  float  round  the  sun,  and 
break  away  sometimes  in  one  place  and  sometimes  in  an- 
other, allowing  us  to  see  down  through  the  gap  into  the 
body  of  the  sun  itself,  which  thus  has  the  appearance  of  a 
dark  spot.  This  is  the  explanation  now  received  by  astro- 
nomers as  most  probable,  and  it  accounts  for  the  constant 
appearance  and  disappearance  of  the  spots. 

In  the  year  1826,  a  well-known  German  astronomer, 
Herr  Schwabe,  of  Dessau  (who  died  in  1874),  determined  to 
take  regular  notes  of  the  periods  when  there  were  most  spots 
to  be  seen  on  the  face  of  the  sun.  Every  day  during  twelve 
years,  when  the  sky  was  clear  enough  for  him  to  observe  the 
sun,  he  examined  it  through  his  telescope,  and  noted  how 
many  spots  he  could  see. 

In  this  way  he  discovered  that  there  was  a  regular  de- 
crease in  the  number  of  spots  for  about  five  years  and  a 
half,  and  then  during  the  next  five  and  a  half  years  a  gradual 
increase,  till  they  were  very  numerous  indeed.  This  led  him 
to  think  that  the  spots  went  through  a  complete  round  01 
cycle  of  changes  in  about  eleven  years  j  but  as  he  found  it 
difficult  to  persuade  other  astronomers  of  the  fact,  he  actually 
carried  on  his  daily  observations  for  twenty  years  longer,  and 
then,  at  the  end  of  thirty-four  years  of  daily  observation,  he 
was  able  to  assert  boldly  that  he  had  established  the  truth  of 
his  theory. 

He  had  now  kept  an  account  of  three  periods  of  eleven 
years.  ■  At  the  beginning  of  each  of  these  periods  the  sun 
was  for  some  time  smooth  and  almost  free  from  spots  ;  then 
from  year  to  year  they  increased,  till,  at  the  end  of  five  and 
a  half  years,  as  many  as  fifty  or  sixty  could  be  seen  at  one 
time.     Then  they  decreased  again  till,  at  the  end  of  another 


CH.  XXXV.  SPOTS  ON  THE  SUJV.  355 

five  and  a  half  years,  the  sun's  face  was  comparatively  smooth 
and  spotless.  During  the  time  that  Schwabe  was  studying 
these  changes,  other  men  in  the  different  observatories  of 
Europe  had  noticed  some  remarkable  peculiarities  about  the 
magnetic  needle.  As  long  ago  as  1722,  a  famous  astronomer 
named  Graham  pointed  out  that  the  magnetic  needle  shifts 
from  side  to  side  a  little  every  day  as  the  sun  passes  from 
one  side  to  the  other  of  the  globe.  The  movement  is  so 
small  that  it  cannot  be  seen  without  very  accurate  instru- 
ments, but  it  shows  that  the  sun's  course  does  affect  the 
magnet ;  and  when  very  careful  notes  began  to  be  made  in 
different  observatories,  it  was  noticed  that  this  daily  shifting 
was  greater  some  years  than  others.  In  1850  an  astronomer 
named  Lamont,  of  Munich,  pointed  out  that  the  movement 
became  greater  each  year  for  about  five  and  a  half  years,  and 
then  grew  less  during  the  same  period  ;  this  led  Sir  Edward 
Sabine  to  suggest  that  perhaps  the  spots  on  the  sun  had 
something  to  do  with  the  magnetic  currents,  since  they  both 
went  through  a  regular  cycle  of  changes  in  about  eleven 
years. 

And  now  comes  a  curious  proof  of  the  truth  of  this 
theory.  In  September  1859,  when  a  famous  sun-gazer, 
Mr.  Carrington,  was  observing  and  measuring  the  spots  on 
the  sun,  he  suddenly  noticed  a  bright  spot  break  out  on  the 
sun's  face  j  and  fortunately  another  observer,  Mr.  Hodgson, 
who  was  in  another  part  of  England,  saw  this  same  spot  at 
the  same  moment.  The  whole  time  from  the  appearance  till 
the  disappearance  did  not  exceed  five  minutes,  but  when 
inquiry  was  made,  it  was  found  that  the  three  magnetic 
needles  at  Kew,  which  keep  a  register  of  their  own  move- 
ments, had  all  been  jerked  strongly  exactly  at  this  time. 
Nor  was  this  all :  the  magnetic  currents  passing  through  our 


356  NINETEENTH  CENTURY.  pt.  iii. 

atmosphere  at  that  moment  set  up  such  strong  electric  cur- 
rents in  the  wires  of  the  telegraphs  all  over  the  world,  that  the 
signalmen  at  Washington  and  Philadelphia  received  severe 
electric  shocks;  a  telegraphic  apparatus  in  Norway  was  set 
on  fire,  and  a  stream  of  electric  light  followed  the  pen  of 
Bain's  electric  telegraph,  which  writes  down  the  message  on 
chemically  prepared  paper.  Moreover,  beautiful  auroras 
were  seen  in  both  hemispheres,  and  these  brilliant  lights  are 
believed  to  be  caused  by  magnetic  currents.  The  magnetic 
storms  on  this  occasion  lasted  for  several  days,  and  there 
could  no  longer  be  any  doubt  that  the  sun  at  a  distance  of 
nearly  92,000,000  miles  can  produce  a  complete  hurricane 
of  magnetic  disturbance  on  our  earth.  This  connection  of 
the  storms  with  the  sun-spots  seems  indeed,  as  I  have  said, 
P-  353>  to  suggest  that  the  sun  must  have  the  power  of  pro- 
ducing magnetic  currents  in  some  more  direct  way  than 
merely  through  the  action  of  electric  currents  set  up  by  the 
varying  heat  on  different  parts  of  the  earth. 

Invention  of  the  Electric  Telegraph  by  Wheatstone  and 
Cooke,  1837. — We  have  spoken  in  the  last  paragraph  of  the 
electric  telegraph,  and  though  this  is  more  strictly  an  inven- 
tion than  a  step  in  science,  yet  we  can  hardly  close  an 
account  of  electricity  and  magnetism  without  showing  how 
the  discovery  of  these  two  forces  has  made  it  possible  for 
our  thoughts  to  be  carried  in  a  few  moments  of  time  across 
land  and  sea  to  the  most  distant  parts  of  the  world. 

Ever  since  Volta  showed,  in  1800,  that  an  electric  current 
can  be  sent  for  any  distance  along  a  wire  the  two  ends  of 
which  are  joined  to  the  poles  of  a  battery,  scientific  men  had 
speculated  whether  it  might  not  be  possible  to  use  this 
current  for  making  signals  at  a  distance.  But  there  was 
always  the  difficulty  of  how  to  make  the  signs  at  the  other 


CH.  XXXV.  WHEATSTONE  AND   COOKE.  357 

end.  In  18 16,  Mr.  Ronalds,  of  Hammersmith,  hung  pith- 
balls  on  to  a  wire,  which  stood  out  while  the  current  was 
flowing,  and  fell  do^vn  again  when  it  ceased;  and  many  other 
such  plans  were  tried,  but  none  succeeded  well. 

When  Oersted,  however,  showed  in  181 9  that  an  electric 
current  will  cause  a  magnetic  needle  to  turn  from  side  to 
side,  it  was  clear  that  here  was  a  means  by  which  signs  could 
be  made  at  any  distance;  and  accordingly  we  find  that 
Ampere,  in  1830,  proposed  to  work  signals  by  a  magnet,  and 
diiferent  attempts  were  made  in  Europe  and  America  to  carry 
out  his  idea.  The  first  electric  telegraph  of  any  value  was 
patented  by  Professor  Wheatstone  and  Mr.  Cooke  in  June 
1837  ;  and  during  the  same  year  Dr.  Steinheil,  of  Munich, 
and  Professor  Morse,  of  America,  both  invented  telegraphs 
of  rather  different  kinds.  I  shall  not  attempt  to  describe 
all  of  these,  but  will  only  explain  the  simplest  principle  of  an 
electric  telegraph  as  it  is  used  in  England,  and  to  show 
how  it  depends  upon  electricity  and  magnetism. 

You  will  see,  if  you  turn  back  to  Figs.  55  and  56,  p.  345, 
that  when  the  electric  current  flowed  round  one  way,  a  b  c 
d,  Fig.  55,  the  north  pole  of  the  needle  turned  to  the  west ; 
when  it  flowed  round  the  other  way,  abed,  Fig.  56,  the  north 
pole  turned  to  the  east.  Now  the  signals  of  the  electric  tele- 
graph depend  upon  this  fact,  that  the  direction  of  the  current 
alters  the  direction  of  the  magnet.  When  one  man  wants 
to  send  a  message  to  another,  he  does  it  by  sending  an 
electric  current  from  a  battery  along  a  telegraph  wire,  so 
that  it  passes  a  magnetic  needle  either  from  right  to  left  or 
from  left  to  right.  When  it  flows  round  one  way,  the  needle, 
even  if  it  is  a  hundred  miles  off,  turns  to  the  right,  when  it 
flows  round  the  other  way  the  needle  turns  to  the  left ;  and 
it  is  agreed  that  so  many  strokes  to  the  right  mean  one 


358  NINETEENTH  CENTURY.  pt.  hi. 

letter,  and  so  many  to  the  left  another  letter,  and  in  this 
way  a  message  can  be  spelt  out,  however  far  off  the  two  men 
maybe.  « 

This  is  the  whole  secret  of  the  electric  telegraph  j  but  to 
understand  how  it  works  you  must  follow  the  explanation  of 
the  two  diagrams  (Figs.  60  and  61),  very  carefully.  Suppose 
that  a  message  is  going  between  London  and  York,  four 
things  are  wanted  to  convey  it: — i.  A  battery  to  produce  an 
electric  current.  2.  A  wire  to  carry  the  current.  3.  A  gal- 
vanometer, that  is  a  box.  A,  a',  holding  a  magnetic  needle  to 
make  the  signs.  4.  A  little  box  called  a  commutator,  b,  b', 
in  which  the  position  of  the  wires  can  be  changed  so  as  to 
send  the  current  first  one  way  and  then  another. 

1.  The  battery  is  an  ordinary  chemical  battery  such  as 
has  already  been  explained. 

2.  The  wire  is  stretched  from  station  to  station,  resting 
on  little  earthenware  cups  to  prevent  the  electricity  running 
down  the  poles  into  the  earth,  and  is  arranged  in  a  coil  round 
the  magnetic  needle  at  each  station  in  such  a  way  that  when 
the  current  flows  from  left  to  right  the  needle  will  turn  to  the 
right,  when  it  flows  from  right  to  left  the  needle  will  turn 
to  the  left.  You  will  observe  that  there  is  only  one  wire  in 
the  diagram,  although  we  know  that  no  current  will  pass 
unless  there  is  a  complete  circuit  from  the  battery,  going 
out  at  one  pole  and  coming  back  to  the  other.  At  first 
telegraphs  were  made  with  a  second  wire  to  return  the 
current,  but  Steinheil  discovered  that  this  is  not  needed, 
for  that,  if  the  ends  of  the  wires  are  sunk  in  the  ground, 
with  plates  of  copper,  f  g,  fastened  to  them,  the  earth 
itself  will  act  as  the  second  wire,  and  carry  back  the  re- 
turn current  to  the  battery.  It  is  not  known  precisely  how 
the  current  returns ;  it  has  been  suggested  that  the  earth  is 


CH.  XXXV. 


THE  ELECTRIC   TELEGRAPH. 


359 


a  great  reservoir,  as  it  were,  of  electricity,  so  that  when  the 
current  runs  into  it  at  one  place  an  equal  amount  must  run 
out  at  another ;  but  all  that  is  really  known  is  that  the  whole 
globe  acts  practically  as  a  return  wire. 

3.  The  magnetic  needle  is  made  of  two  or  more  parts,  for 
since  it  would  be  very  inconvenient  if  the  pointer  were  always 
trying  to  turn  to  the  north,  this  is  avoided  by  fastening  two 
needles  side  by  side,  with  the  north  pole  of  the  one  lying 

Fig.  60. 


yiiiiiiH 


Fig.  61. 


LDh/OON 


YORK 


Diagrams  showing  the  general  principle  of  the  Electric  Telegraph.    • 

A,  a',  Galvanometer,  or  box  containing  the  magnetic  needle.  B,  b'.  Commutator,  or 
box  in  which  the  telegraph  wire  and  earth  wire  are  joined  to  each  other  as  in  a', 
or  to  the  battery,  as  in  b.  c,  d,  Telegraph  wire,  e.  Earth  wire,  f,  g.  Copper 
plates  at  the  end  of  the  earth  wire.  The  arrows  show  the  direction  of  the  positive 
current. 

against  the  south  pole  of  the  other,  and  thus,  as  the  earth 
attracts  each  needle  in  a  different  way,  the  pull  is  neutralized. 
This  double  needle  is  called  aa'asfatic  needle,  and  it  is  so 
placed  in  the  box  a  in  the  form  of  telegraph  Vv^e  are  de- 
scribing, that  one  needle  is  inside  surrounded  by  the  wire, 
-while  the  other  is  outside  on  the  face  of  the  box. 


36o  NINETEENTH  CENTURY.  pt.  hi. 

4.  The  com7nutatoi%  b,  is  a  box  with  an  apparatus  inside 
which  is  so  arranged  that  by  turning  a  handle  (not  shown 
in  the  diagram)  different  ways  the  earth  wire  and  telegraph 
wire  can  be  joined  together,  or  either. of  them  can  be  joined 
to  one  of  the  poles  of  the  battery. 

The  commutator  and  galvanometer  are  really  made  in 
one  instrument,  but  I  have  drawn  them  separate  to  make  it 
more  clear. 

Now,  when  the  man  in  London  wants  to  send  his  message 
to  York,  he  first  sends  off  a  current  which  rings  a  little  bell 
at  all  the  stations  along  the  line  to  call  attention,  and  then 
spells  out  the  word  York.  This  warns  the  man  at  that 
station  to  turn  the  handle  of  his  commutator,  b',  so  that  the 
telegraph-wire,  d^  and  the  earth- wire,  g,  are  joined  together. 
Then  the  message  can  be  sent.  The  man  in  London  turns 
his  handle  according  as  he  wishes  the  current  to  go.  In 
Fig.  60  he  has  turned  it  so  that  the  telegraph  wire,  c,  is 
joined  to  the  positive  pole  of  the  battery,  and  the  current 
will  pass  above  ground  along  c  d  to  the  galvanometer  a', 
turning  the  needle  to  the  right,  and  will  then  go  back  through 
the  earth  hy  g/e  to  the  battery.  But  in  Fig.  61  the  man 
has  altered  the  handle,  and  now  the  earth  wire,  e,  is  joined 
to  the  positive  pole,  and  so  the  current  passes  underground 
Sit  e  f,  and  out  at^,  and  entering  the  galvanometer  on  the 
left  side,  turns  the  needle  to  the  left,  and  goes  back  by  the 
telegraph  wire,  d  c,  to  the  battery.  In  this  way  he  turns  it 
from  right  to  left  as  he  will,  and  spells  out  the  message  thus : 
Left,  right  J  =  A ;  left,  right,  left,  left,  ^/^^  =  L;  left,  right, 
right  ,//  =  W ;  left,  \  =  E  ;  therefore  J  ;  J,  ;  J,  ;  J/; 
v;  ^\^^^  v/u  3  spells  '  all  wellJ 

It  is  not  necessary  to  have  a  separate  wire  for  every  tele- 
graphic station :  one  wire  will  do  all  the  work  so  long  as  it  is 


CH.  XXXV.         THE  AMERICAN  TELEGRAPH.  361 

only  used  by  one  man  at  a  time.  Therefore  at  every  station 
there  is  a  galvanometer  to  point  out  the  message,  a  battery 
to  provide  the  current,  and  a  commutator  to  change  the 
current ;  but  these  are  not  joined  to  the  general  wire  unless 
they  are  being  used.  In  Morse's  American  telegraph,  which 
is  generally  used  on  the  Continent,  the  needle  pricks  holes 
in  a  strip  of  paper,  so  that  the  message  can  be  kept,  and 
Bain's  electro -chemical  telegraph  writes  down  the  marks  on 
chemical  paper.  But  all  these  are  only  improvements  of  the 
same  principle  by  which  an  electric  current  going  first  one 
way  and  then  another  acts  on  a  magnetic  needle. 


Chief  Works  consulted.  —  Lardner's  *  Cyclopaedia '  —  '  Electricity, 
Magnetism,  and  Meteorology;'  'Annals  of  Philosophy,'  New  Series, 
1822,  vols.  ii.  and  iii.  ;  'History  of  Magnetism  ;'  'Encyclopaedia  Me- 
tropolitana,' art.  '  Electro -Magnetism  ;' Faraday's  'Experimental  Re- 
searches in  Electricity,'  1859;  Tyndall's  '  Faraday  as  a  Discoverer ; ' 
Gladstone's  '  Michael  Faraday  ; '  *  Nouvelle  Biog.  Universelle ' — *  Am- 
pere,' 'Oersted'  ;  Ampere,  '  Observations  Electro-dynamiques,'  1822; 
Faraday,  '  Various  Forces  of  Nature  ; '  Proctor,  *  The  Sun  ; '  Her- 
schel's  '  Familiar  Lectures  ; '  Brande's  *  Manual  of  Chemistry.' 

IT 


362  NINETEENTH  CENTURY,  pt.  Iir. 


CHAPTER  XXXVI. 

SCIENCE    OF   THE   NINETEENTH    CENTURY   (CONTINUED). 

Davy  discovers  that  Nitrous  Oxide  produces  Insensibility — Laughing- 
gas — Safety-lamp,  1815 — Nicholson  and  Carlisle  discover  Decom- 
position of  Water,  1800 — Davy  discovers  the  effect  of  Electricity 
upon  Chemical  Affinity— Faraday's  Discoveries  in  Electrolysis — 
Indestructibility  of  Force — Various  modes  discovered  of  Decompos- 
ing Substances — John  Dalton,  Chemist — Law  of  Definite  Propor- 
tions— Law  of  Multiple  Proportions — Dalton's  Atomic  Theory — 
The  study  of  Organic  Chemistry — Liebig  the  great  Teacher  in 
Organic  Chemistry. 

Sir  Humphry  Davy,  1778-1829. — We  saw  in  the  last 
chapter  how  Oersted,  Davy,  Ampere,  Faraday,  and  Seebeck, 
by  their  various  discoveries,  showed  the  connection  between 
Electricity,  Magnetism,  and  Heat.  We  must  now  learn  how 
the  connection  between  electricity  and  chemical  change  was 
also  worked  out.  This  was  done  by  Sir  Humphry  Davy  and 
Faraday,  who  thus  put  England  once  more  at  the  head  of 
chemical  discovery,  in  which  the  French  school  of  Lavoisier 
had  so  long  taken  the  lead.  • 

Sir  Humphry  Davy,  whom  we  have  mentioned  before  as 
making  experiments  upon  heat,  was  born  in  1778,  at  Pen- 
zance, in  Cornwall,  and  died  at  Geneva  in  1829.  His  mother 
being  a  widow,  he  was  apprenticed  when  quite  young  to 
an  apothecary,  and  there  with  wine  glasses,  old  medicine 
bottles,  tobacco  pipes,  and  a  syringe,  he  made  his  first 
chemical  experiments.     When  he  was  scarcely  twenty  years 


CH.  xxxvL  SIR  HUMPHREY  DAVY.  363 

of  age,  Dr.  Beddoes,  a  physician,  who  had  opened  a  hospital 
for  curing  patients  by  the  use  of  different  gases,  heard  so 
much  of  the  young  man's  abilities  that  he  invited  him  to 
come  to  Bristol;  where  he  employed  him  in  making  experi- 
ments. 

In  this  way  Davy's  attention  was  drawn  to  nitrous  oxide, 
a  gas  which  had  been  declared  by  a  celebrated  physician, 
Dr.  Mitchell,  to  be  very  poisonous.  Our  young  chemist 
wanted  to  try  this  for  himself,  and  actually  began  breathing 
it  in  small  quantities  to  see^whether  it  would  affect  him.  He 
proved  that  it  certainly  was  not  so  poisonous  as  Mitchell  had 
thought,  and,  growing  gradually  bolder  and  bolder  in  the  use 
of  it,  he  succeeded  at  last  in  breathing  the  gas  for  several 
minutes,  at  the  end  of  which  time  he  lost  all  consciousness, 
and  found  himself  in  a  land  of  delicious  dreams,  out  of  which 
he  awoke  gradually  without  being  injured  in  any  way.  En- 
chanted at  having  discovered  such  a  delightful  sensation,  he 
carried  on  his  experiments  for  more  than  ten  months,  and 
when  he  published  the  results,  and  told  the  world  that  the 
mere  breathing  of  a  gas  could  make  a  man  sleep,  and  dream, 
and  laugh  without  any  cause,  it  created  a  great  sensation, 
and  Davy's  name  soon  became  well  known. 

At  this  time  (iSoi)  the  Royal  Institution  had  just  been 
founded,  and  Count  Rumford,  seeing  that  Davy  was  a  young 
man  of  great  talent,  offered  him  the  appointment  of  Assistant- 
chemist.  Davy  accepted  it,  and  from  that  time  devoted  himself 
entirely  to  science.  He  was  young,  bright,  and  enthusiastic, 
and  his  lectures  were  so  clear  and  eloquent,  that  the  Royal 
Institution  soon  became  famous  under  his  influence,  while 
every  new  appliance  for  making  chemical  experiments  was 
given  him  in  his  laboratory.  It  was  here  that  he  made  his 
observations  on  flame  in  181 5,  and  constructed  his  Safety- 


364  NINETEENTH  CENTURY.  vr.  111. 

lamp,  which  has  saved  so  many  lives,  and  for  the  invention 
of  which  he  received  the  title  of  baronet.  It  was  here  also 
that  he  made  his  first  experiments  in  electro-chemistry,  which 
is  the  only  one  of  his  many  discoveries  of  which  we  can  speak. 

Discovery  of  Electrolysis,  or  the  Decomposition  of 
Water  by  an  Electric  Current,  1800-1806. — In  the  year 
1800,  two  men  named  Nicholson  and  Carlisle  discovered  by 
chance  that  when  the  two  wires  of  a  voltaic  battery  were 
dipped  in  water,  bubbles  of  gas  rose  np  from  them.  They 
also  found  by  experiment  that  the  gas  from  one  wire  was 
oxygen,  and  from  the  other  hydrogen;  but  where  these  gases 
came  from,  whether  they  were  produced  by  the  electricity,  or 
came  from  the  battery,  or  from  the  water,  they  could  not 
tell.  Moreover,  besides  the  oxygen  and  hydrogen  which 
came  off,  there  also  appeared  an  acid  of  some  kind  at  the 
positive  pole,  as  was  shown  by  damp  litmus  paper  turning 
red  (see  p.  229),  and  an  alkali  appeared  at  the  negative  pole 
which  turned  this  red  litmus  paper  blue  again.  This  looked 
as  if  the  electric  current  had  produced  something  in  the 
water,  for  Cavendish,  as  you  will  remember,'  had  shown 
that  pure  water  is  made  of  oxygen  and  hydrogen  only  (see 
p.  231).  Many  chemists,  therefore,  set  themselves  to  try 
to  discover  what  effect  the  electric  current  had  on  the 
water,  and  Davy  in  1806  succeeded  in  solving  the  question. 

The  history  of  his  experiments  is  especially  interesting 
because  it  shows,  as  we  have  noticed  so  often  before,  that  a 
patient  and  careful  inquiry  into  nature  always  gains  a  true 
answer  in  the  end.  Davy  did  not  believe  that  the  electric 
current  produced  anything  in  the  water ;  he  thought  that 
both  the  acid  and  the  alkali  came  from  the  vessels  that  were 
used.  So  he  set  to  work  steadily  to  clear  away  all  possibility 
of  impurities.     He  took  distilled  water,  and  used  cups  first 


CH.  XXXVI.  ELECTROLYSIS,  365 

made  of  agate,  and  afterwards  of  pure  gold,  because  he 
found  that  the  clay  of  the  china  cups  was  acted  upon  by  the 
current.  Yet,  in  spite  of  these  and  many  other  precautions, 
the  acid  and  the  alkali  still  continued  to  appear.  Then  he 
used  water  which  he  had  evaporated  very  slowly,  instead  of 
distilling  it,  because  he  found  that  distilled  water  carried 
away  some  salt  with  it.  When  he  had  done  this  the  acid  was 
weaker,  but  the  alkali  was  as  strong  as  ever.  At  this  point 
it  occurred  to  him  that  the  alkali  might  perhaps  come  out 
of  the  air,  so  he  put  his  gold  cups  of  water  under  an  air- 
pump,  and  completely  exhausted  the  air,  filling  the  pump 
with  hydrogen  to  make  quite  sure  that  no  other  gas  could  be 
left  in.  When  he  had  tried  this  several  times  and  made  it 
perfect  in  every  way,  he  succeeded  at  last  in  getting  nearly 
pure  oxygen  at  one  pole  and  hydi'ogen  at  the  other. 

By  this  experiment  Davy  not  only  confirmed  Cavendish's 
discovery  that  pure  water  is  made  of  hydrogen  and  oxygen, 
but  he  also  established  a  totally  new  method  of  analysing 
substances,  and  finding  out  the  materials  of  which  they  are 
composed.  This  method  was  in  some  ways  more  certain  than 
Bergmann's  method  of  tests,  for  when  you  drive  one  ele- 
ment out  by  putting  another  in  its  place,  you  have  some 
difficulty  in  finding  out  exactly  what  has  happened ;  but 
when  a  substance  is  decomposed  by  electricity  you  literally 
take  it  to  pieces,  and  see  the  elements  of  which  it  consists. 

Discovery  of  Potassmm  and  Sodium. — Having  suc- 
ceeded in  the  case  of  water,  Davy  now  went  on  to  try 
the  efi"ect  of  the  electric  current  on  other  bodies,  and 
the  first  which  he  took  were  common  potash  and  soda, 
which  had  always  been  supposed  to  be  simple  substances, 
which  could  not  be  decomposed.  For  several  reasons,  how- 
ever, Davy  believed  that  it  would  be  possible  to  reduce  them 


366  NINETEENTH  CENTURY.  pt.  hi. 

into  more  than  one  substance.  So  he  heated  some  pure 
potash  in  a  spoon  until  it  was  quite  liquid,  and  fastening 
the  two  ends  of  the  spoon  to  the  wires  of  a  battery,  he  sent 
an  electric  current  through  it.  After  a  little  while  the  potash 
began  to  be  agitated,  and  to  rise  up  in  bubbles,  and  then 
there  came  to  the  surface  beautiful  silver-like  globules,  some 
of  which  burst  into  flame,  while  others  remained  covered 
by  a  sort  of  white  film. 

'  Davy's  delight,'  writes  his  brother,  '  when  he  saw  the 
minute  shining  globules  like  mercury  burst  through  the 
crust  of  potash  and  take  fire  as  they  reached  the  air, 
was  so  great  that  he  could  not  contain  his  joy— he  actually 
bounded  about  the  room  in  ecstatic  delight.'  It  must  indeed 
have  been  a  beautiful  sight  in  itself ;  but  probably  Davy's 
excitement  arose  chiefly  from  the  new  truth  he  saw  in  it. 
He  had  proved  that  potash  was  not  a  simple  substance, 
but  contained  something  which  had  never  before  been 
discovered. 

At  first  he  had  great  difiiculty  in  collecting  the  globules, 
for  they  not  only  burst  into  flame  when  they  met  the  air,  but 
even  in  water  they  took  fire,  joining  themselves  to  the  oxygen 
and  setting  the  hydrogen  free.  At  last,  however,  he  succeeded 
in  collecting  them  in  rock  oil,  or  naphtha,  which  contains  no 
oxygen.  He  was  then  able  to  examine  them,  and  he  found 
they  were  composed  of  a  metal  hitherto  quite  unknown,  to 
which  he  gave  the  name  of  potassiwn.  A  few  days  later  he 
procured  the  metal  sodium  out  of  common  soda  by  the  same 
process. 

This  method  of  decomposing  substances  is  called  electro- 
lysis^ which  means  '  setting  free  by  electricity.'  Davy  made 
use  of  it  to  decompose  many  earths,  such  as  lime,  mag- 
nesia, &c.,  and  the  great  Swedish  chemist,  Berzelius  (bom 


CH.  XXXVI.  FARADA  TS  EXPERIMENTS.  367 

1778,  died  1848),  discovered  several  new  chemical  sub- 
stances by  means  of  it. 

Faraday's  Experiments  on  the  Connection  between 
Electricity  and  Chemical  Affinity. — This  was  the  practical 
use  of  the  discovery;  but  it  had  another  gi-eat  interest  for 
chemists,  because  it  proved  that  electricity  can  overcome 
that  power  called  '  chemical  affinity/  which  holds  two  or 
more  elements  together  in  one  compound  substance.  You 
will  remember  that  Bergmann,  and  indeed  Newton  before 
him,  pointed  out  that  there  is  some  force  which  causes 
certain  bodies  to  choose  each  other  out  when  they  meet,  and 
to  unite  firmly  so  as  to  become  a  new  substance  which 
has  its  own  peculiar  characters.  Chlorine  and  sodium,  for 
example,  when  heated,  unite  to  form  common  salt,  Avhich  is 
not  the  least  like  either  chlorine  or  sodium  when  they  are 
separate ;  and  in  the  same  way  hydrogen  and  oxygen  unite 
to  form  water.  In  these  new  states  they  are  held  together 
by  a  power  which  for  want  of  a  better  name  we  call 
'  chemical  attraction,*  or  '  chemical  affinity '  (see  p.  229). 

Now  Davy  showed  that  an  electric  current  conquers 
this  power  and  sets  the  different  elements  free,  so  that  they 
can  each  go  their  own  way.  Thus  the  electric  current 
passing  through  the  water  overcomes  the  force  which  holds 
the  oxygen  and  hydrogen  together,  so  that,  at  the  point 
where  the  battery  wires  touch  the  water,  hydrogen  bubbles 
come  off  on  one  side  and  oxygen  on  the  other. 

It  is  to  Faraday,  however,  that  we  owe  most  of  our 
knowledge  about  the  intimate  connection  between  electricity 
and  chemical  change.  He  followed  up  Davy's  experiments, 
and  traced  out  very  clearly  the  cause  and  effect  of  the 
chemical  current.  He  showed  in  the  first  place  that  a  sub- 
stance cannot  be  decomposed  by  electricity  unless  it  is  a 


368  NINETEENTH  CENTURY.  pt.  hi. 

good  conductor,  so  that  the  current  passes  readily  along  it. 
Thus,  ice  being  a  bad  conductor,  the  slightest  film  of  ice 
interposed  between  the  water  and  the  electric  wires  will  pre- 
vent the  current  from  setting  free  the  oxygen  and  hydrogen  j 
and  ether  and  alcohol  cannot  be  decomposed  at  all  by  elec- 
tricity, because  they  will  not  conduct  the  current. 

He  also  showed  that  the  electric  current  itself  does  not 
depend  upon  any  effect  which  the  two  metals  have  directly 
upon  each  other,  as  Volta  thought,  but  is  caused  by  the 
chemical  action  going  on  between  the  zinc  and  the  water. 
Thus,  if  you  put  some  zinc  in  sulphuric  acid  and  water,  the 
zinc  pulls  the  water  to  pieces,  and  hydrogen  gas  comes  bub- 
bling off,  but  if  you  coat  the  zinc  with  mercury,  hydrogen 
will  no  longer  come  off,  and  no  action  will  take  place  till 
you  put  another  metal  in  the  water,  as  for  example  a  piece 
of  copper  and  connect  the  two  metals  by  a  wire.  Then  the 
hydrogen  bubbles  off  again,  but  this  time  it  does  not  come 
off  the  zinc,  hut  off  the  copper.  The  force  which  overcomes 
the  chemical  attraction  in  the  water  has  been  made  to  travel 
across  the  vessel  from  one  metal  to  the  other,  and  this 
journey  may  be  made  as  long  a  one  as  you  choose,  and 
may  even  be  continued  for  hundreds  of  miles  if  only  the 
current  has  some  means  of  finding  its  way  home  to  the  first 
metal  at  last. 

Now  all  this  is  a  modified  result  of  the  chemical  action 
of  the  zinc  and  acid  water  upon  each  other;  as  Faraday 
proved  in  a  most  beautiful  way  by  showing  that  the  power 
of  the  electric  current  to  decompose  water  in  another  vessel 
depends  entirely  upon  the  violence  of  the  action  going  on 
between  these  two  elements  of  the  battery.  If  the  battery 
is  weak,  the  water  in  which  the  ends  of  the  wires  are  dipped 
is  decomposed  slowly ;  if  the  battery  is  strong,  the  bubbb  s 


CH.  XXXVI.        THE  STUDY  OF  CHEMISTRY.  369 

of  oxygen  and  hydrogen  come  off  rapidly  and  vehemently. 
This  led  him  to  invent  a  useful  little  instrument  called  a 
voltameter^  which  measures  the  quantity  of  water  decom- 
posed, and  so  tells  exactly  what  is  the  strength  of  the 
electric  current.  'Thus  we  see/  says  Faraday  in  one 
of  his  lectures,  '  that  the  power  which  decomposes  water, 
or  produces  the  heat  and  light  of  the  electric  spark,  is 
neither  more  nor  less  than  the  chemical  force  of  the  zinc — 
its  very  force  carried  along  the  wires  and  conveyed  to 
another  place.' 

And  here  again  we  find  ourselves  brought  face  to  face 
with  the  truth  that  all  the  various  physical  forces  are  only 
different  forms  of  one  and  the  same  force.  We  learnt  before 
that  motion  can  be  turned  into  heat  and  heat  into  motion, 
while  heat,  magnetism, .  and  electricity  all  in  the  same  way 
give  rise  to  each  other ;  and  now  we  learn  that  chemical 
change  gives  rise  to  electricity,  and  electricity  in  its  turn  to 
chemical  change.  So  that  the  whole  set  of  physical  forces, 
heat,  motion,  electricity,  magnetism,  and  chemical  change, 
are  all  different  phases  of  one  indestructible  force  which  we 
lose  sight  of  in  one  shape,  only  to  find  it  in  another. 

Methods  of  Studying  Chemistry. — ^We  have  now  learnt 
how  most  of  the  chief  methods  of  producing  chemical 
change  have  been  worked  out.  The  science  of  chemistry 
consists  in  using  these  methods  to  test  and  decompose  all 
the  substances  in  our  earth  and  atmosphere,  and  so  learning 
their  nature. 

We  have  seen  that  there  are  four  ways  of  thus  analysing 
compound  bodies.  First,  by  testing  them  with  other  sub- 
stances which  attract  some  of  their  elements,  and  draw  them 
out  of  the  compound,  as  when  by  plunging  a  piece  of  iron 
into  nitrate  of  copper  the  iron  attracts  the  nitric  acid  and 


570  NINETEENTH  CENTURY.  ft.  hi. 

draws  it  out,  leaving  the  copper  to  fall  down  as  a  metal. 
This  was  the  method  chiefly  worked  out  by  Bergmann  in 
1761,  and  which  has  since  then  been  brought  to  much 
greater  perfection  by  other  chemists. 

Secondly,  by  heating  substances  gently  and  examining 
the  vapours  which  rise  from  them,  and  afterwards  analysing 
what  remains  by  burning.  This  method  was  fairly  under- 
stood by  Geber,  and  was  first  applied  to  organic  substances 
by  Boerhaave. 

Thirdly,  by  passing  an  electric  current  through  a  com- 
pound substance  in  a  fluid  state,  and. so  overcoming  the 
force  which  holds  the  different  elements  together  and 
setting  them  free.  This  method,  called  electrolysis^  was  dis- 
covered by  Davy  in  1806,  and  afterwards  thoroughly  worked 
out  by  Faraday. 

Fourthly,  there  is  the  method  of  spectrum  analysis 
suggested  by  Herschel  in  1822,  which  was  carried  on  with 
great  success  by  Bunsen  and  Kirchhoff".  In  this  method 
the  substance  is  turned  into  gas  either  by  ordinary  heat  oir 
by  the  electric  spark,  and  is  then  examined  by  the  spectro- 
scope j  the  elements  being  determined  by  the  position  of 
the  bright  lines  they  throw  on  the  spectrum. 

There  is  still  a  fifth  method,  about  which  we  have 
said  nothing  as  yet,  and  which  was  chiefly  brought  into  use 
by  the  chemist  Berzelius  (mentioned  p.  366),  namely  the 
fusing  of  substances  by  means  of  the  blowpipe.  This 
instrument  is  merely  a  little  tube  with  a  mouthpiece  at  one 
end  and  a  very  minute  hole  at  the  other.  By  placing  the 
minute  hole  in  the  middle  of  a  flame  and  blowing  through 
the  mouthpiece,  the  centre  of  the  flame  is  made  to  burn 
furiously,  and  many  substances  can  be  melted  and  decom- 
posed by  it  which  do  not  yield  to  ordinary  heat. 


CH.  XXXVI.  JOHN  DALTON.  371 

By  these  different  methods  a  very  large  number  of  sub- 
stances have  been  analysed  since  the  time  of  Davy  and 
Faraday,  and  sixty-four  elements  or  simple  substances  have 
been  discovered.     It  is  possible  that  some  of  these  may 
even  at  some  future  time  be  decomposed  and  shown  to  be 
made  up  of  two  elements ;  we  can  only  affirm  that  now  they 
appear   to   us   to   be   simple   substances.     Some   of  these 
elements  have  been  brought  together  and  made  to  unite 
into  compound  substances   by  artificial   means  ;  as  when, 
for  instance,  oxygen  and  hydrogen  mixed  and  lighted  by 
a  spark  rush  together  and  form  water,  or  when  hydrogen 
and  chlorine  mixed  together  and  placed  in  the   sunlight 
unite  to  form  hydrochloric  acid.^     This  method  of  bringing 
elements  together  to  form  a  compound  substance  is  called 
synthesis^  and   is  exactly  the  opposite  of  analysts,   or   the 
splitting  up  of  a  compound  substance  into  its  elementary 
parts. 

To  follow  out  the  gradual  development  of  synthesis  and 
analysis,  and  to  see  how  all  the  different  elements  and  com- 
pounds were  in  this  way  determined,  would  be  to  write  a 
work  upon  chemistry.  There  is  only  one  other  general 
principle  which  we  ought  to  try  and  understand  here ; 
namely,  the  proportions  in  which  the  elements  combine  to 
form  substances.  This  principle,  which  lies  at  the  root  of 
all  our  modern  chemistry,  was  first  worked  out  by  a  poor 
schoolmaster  named  Dalton. 

Dalton  shows  that  the  Different  Chemical  Elements 
always  Combine  in  Definite  Proportions. — John  Dalton 
was  bom  of  Quaker  parents  in  1766,  near  Cockermouth,  in 

'  Sir  H.  Davy  was  the  first  to  discover,  in  1807,  that  hydrochloric 
acid  is  made  merely  of  hydrogen  and  chlorine  ;  before  then  it  was 
believed  that  every  acid  must  have  oxygen  in  it. 


372  NINETEENTH  CENTURY.  rx.  in. 

Cumberland.  He  received  the  ordinary  education  of  a  village 
school,  and  after  being  master  of  a  small  academy  at  Kendal, 
he  went  to  Manchester,  where  he  supportect  himself  all  the 
rest  of  his  life  by  teaching  mathematics. 

Fortunately  for  science,  a  blind  gentleman  named  Gough 
became  interested  in  him,  and  gave  him  the  use  of  his 
library  and  chemical  laboratory,  which  enabled  Dalton  to 
work  out  many  useful  facts,  and  to  establish  the  laws  which 
are  now  the  guide  of  all  chemists,  though  they  differ  about 
some  of  his  conclusions. 

You  will  remember  that  it  was  only  in  the  time  of 
Lavoisier  that  chemists  began  to  weigh  carefully  the  gases 
into  which  substances  can  be  decomposed.  Before  then  it 
had  been  thought  sufficient  to  say  that  a  substance  contained 
sulphur,  mercury,  carbon,  &c.,  without  saying  how  much  of 
it  there  was.  But  after  the  discovery  of  oxygen,  when  the 
real  nature  of  chemical  change  began  to  be  understood, 
chemists  saw  the  importance  of  weighing  accurately  the 
different  elements  into  which  a  substance  can  be  broken  up ; 
and  when  this  had  been  done  for  some  time,  and  a  great 
number  of  analyses  had  been  made,  it  was  seen  that  any 
given  chemical  compound  always  contains  the  same  elements 
combined  in  the  same  proportion. 

Thus,  for  example,  all  water,  whether  it  comes  from  rain, 
snow,  dew,  steam,  or  exploded  oxygen  and  hydrogen,  will 
always  be  found  to  contain  two  parts  by  weight  of  hydrogen 
to  sixteen  parts  by  weight  of  oxygen  ;  so  that  if  you  decom- 
pose 1 8  ounces  of  water  you  will  collect  « 

2  volumes  of  hydrogen  weighing  i  oz.  each      .         .       2  ozs. 
I  volume  of  oxygen  weighing  i6  ozs.        .         .         .     i6  ozs. 

1 8  ozs. 


CH.  xxxvi.       LAW   OF  DEFINITE  PROPORTIONS.  373 

And  this  never  varies.     Again,  if  you  take  some  ammonia 
and  decompose  1 7  ounces  of  it  you  will  collect 

3  volumes  of  hydrogen  weighing  I  oz.  each      .         .       3  ozs. 
I  volume  of  nitrogen  weighing  14  oz.       .         .         .14  ozs. 


17  ozs. 


And  this  again  never  varies.  Wherever  you  get  ammonia  it 
will  always  be  made  up  of  these  proportionate  weights  of 
hydrogen  and  nitrogen. 

This  combination  of  the  different  elements  in  fixed 
quantities  is  called  the  law  of  definite  proportions.  It  was 
hinted  at  by  four  chemists  before  Dalton  j  namely  Proust, 
Wenzel,  Higgins,  and  Richter,  but  it  was  very  little  under- 
stood, and  some  eminent  chemists,  such  as  Berthelot,  even 
doubted  whether  it  was  true.  Dalton,  however,  made  a  re- 
markable discovery  which  both  proved  the  truth  of  the  law 
itself  and  showed  that  it  meant  a  great  deal  more  than  had 
been  imagined. 

He  found  that  not  only  are  the  elements  in  any  one 
substance  always  in  a  fixed  proportion,  but  that  each  ele- 
ment, such  as  oxygen,  has  a  weight  of  its  own,  and  will 
only  combine  with  other  elements  in  proportions  of  this 
fixed  weight.  For  example,  oxygen  will  join  itself  to 
nitrogen  in  five  different  proportions,  making  five  different 
substances,  and  in  each  case  the  same  fixed  weight  of  oxy- 
gen is  added.     Thus,  if  you  decompose  22*4  litres  of 

Volumes  of  Weighing 

Nitrogen      Oxygen     Nitrogen  Oxygen 

Nitrous  oxide,  you  will  get  2 
Nitric  oxide  ,,  2 

Nitrous  acid  ,,  2 

Nitric  peroxide         , ,  2 

Nitric  acid  ,,  2 

So  that  each  substance  contains  one  more  volume  of  oxygen 


.     .    I 

.   28 

grammes 

16  grammes 

.       .     2 

.   28 

5> 

32 

•     •    3 

.   28 

>J 

48        „ 

.     .    4 

.   28 

>> 

64        „ 

.     •    5 

.   28 

>  J 

80        „ 

374  NINETEENTH  CENTURY.  pt.  hi, 

compared  to  the  nitrogen  than  the  one  before  it  j  and  this 
volume  always  weighs  i6  grammes^  while  each  volume  of 
nitrogen  weighs  14  grammes. 

Oxygen  behaves  in  this  way  in  all  compounds,  only 
joining  itself  to  other  elements  in  weights  of  16  or  multiples 
of  16.  Thus,  if  you  heat  mercury  as  Lavoisier  did,  so  that 
it  takes  up  oxygen  out  of  the  air,  200  parts  by  weight  of 
mercury  will  combine  with  16  of  oxygen  and  no  more.  If 
you  heat  carbon  with  oxygen,  1 2  parts  by  weight  of  carbon 
will  take  up  16  of  oxygen  to  make  carbonic  oxide,  or  twice 
16=32  to  make  carbonic  acid,  but  it  will  not  take  up  any- 
thing between  these  weights.  This  same  law  holds  true  of 
all  the  elements,  each  one  having  its  own  peculiar  weight. 
Nitrogen,  for  example,  combines  in  weights  of  14,  or  twice 
14=28,  or  three  times  14=42,  &c.  \  sodium  in  weights  of 
23,  46,  and  69,  &c.  This  is  called  the  law  of  mtdtiple  pro- 
portmis,  which  we  owe  entirely  to  Dalton,  and  it  is  a  fact 
about  which  all  chemists  agree.  Dalton  went  on  to  try  and 
explain  it  by  a  theory  which  is  still  a  matter  of  speculation, 
and  which  some  chemists  do  hot  receive. 

Dalton's  Atomic  Theory,  1808. — In  order  to  explain  why 
each  element  should  have  its  fixed  weight  in  which  it  always 
combines,  Dalton  imagined,  as  Democritus,  Epicurus,  Bacon, 
and  Newton  had  done  before  him,  that  all  matter  is  com- 
posed of  tiny  parts,  or  atoms,  which  are  too  small  to  be  seen 
and  which  cannot  be  divided.  These  atoms,  which  he 
pictured  to  himself  as  round  grains  like  very  small  shot, 
would  be  of  the  same  size  in  every  substance,  but  not  of  the 
same  weight.  Hydrogen  atoms  would  be  the  lightest  of 
all,  for  hydrogen  is  the  lightest  substance  known ;  oxygen 
atoms  would  be  16  times,  and  nitrogen  14  times,  as  heavy 
as  those  of  hydrogen. 


CH.  XXXVI.  THE  ATOMIC  THEORY.  375 


Now  when  two  elements  combine  together  they  cannot 
take  up  less,  according  to  Dalton,  than  one  atom  of  each,  or 
two  atoms  of  one  to  one  of  the  other,  and  so  on,  and  there- 
fore exactly  the  weight  of  an  atom  of  any  substance  will 
always  be  added.  For  example,  to  turn  back  to  our  table 
on  p.  373,  Dalton  wOuld  say  that  a  molecule^  or  the  smallest 
portion  which  can  be  imagined,  of  nitrous  oxide  will  contain 
2  atoms  of  nitrogen  weighing  14  each  to  i  atom  of  oxygen 
weighing  16  ;  while  nitric  acid  will  contain  2  atoms  of  nitro- 
gen =  28,  and  5  atoms  of  oxygen,  5  x  16=80.  If  half  an 
atom  of  oxygen  could  be  added,  then  it  might  be  possible 
to  take  up  16  +  8,  or  24  parts  of  oxygen;  but  as  the  atoms 
are  supposed  to  be  indivisible,  this  cannot  be  done,  but  a 
whole  atom  weighing  16  must  be  added  each  time.  There- 
fore you  wdll  see  that  by  an  atom  Dalton  meant  the  smallest 
quantity  of  any  ele7nent  ivhich  can  combine  with  other  sub- 
stances. 

Thus,  water  is  made  up  of  molecules,  each  containing 
two  atoms  of  hydrogen  and  one  of  oxygen.  But  as  these 
atoms  cannot  be  seen,  how  can  it  be  known  how  many  there 
are  in  any  substance,  and  when  we  have  arrived  at  the 
smallest  weight  of  any  element  ?  Dalton  knew  it  in  some- 
thing like  the  following  way  : — 

If  you  decompose  water  by  electricity,  you  know  that  you 
will  collect  two  bottles  of  hydrogen  for  one  of  oxygen.  But 
you  can  also  decompose  it  another  way  :  if  you  take  a 
small  piece  of  the  metal  sodium  and  float  it  on  water,  it  will 
roll  round  and  round  fizzing  violently.  This  is  because 
sodium  joins  very  readily  to  oxygen,  and  the  sodium  is 
turning  out  some  of  the  hydrogen  from  the  water  and  taking 
its  place.  When  the  piece  of  sodium  has  disappeared,  if 
you  evaporate  off  the  rest  of  the  water,  you  will  have  a  white 


37<5  NINETEENTH  CENTURY.  pt.  hi. 


powder,  which  is  caustic  soda  \  and  if  you  dec.ompose  this 
soda,  you  will  get  out  of  it  one  measure  of  hydrogen,  one  of 
oxygen,  and  one  of  sodium.  The  sodium,  you  observe,  has 
turned  exactly  half  the  hydrogen  out  of  the  water  and  taken 
its  place  \  and  this  shows  there  must  have  been  two  atoms 
of  hydrogen  in  the  water,  because  a  single  atom  could  not 
have  been  divided. 

In  the  soda  we  have  now  got  the  smallest  quantity  of 
each  element — sodium,  oxygen,  and  hydrogen — which  will 
combine  with  any  other.  You  can  turn  either  of  these 
three  out  of  the  soda,  but  you  cannot  turn  out  a  part  of  any 
one  of  them.  Therefore,  a  molecule  of  soda  is  said  to  be 
made  of  one  atom  of  hydrogen  weighing  i,  one  atom  of  oxy- 
gen weighing  1 6,  one  atom  of  sodium  weighing  23,  and  these 
numbers  are  called  the  atomic  weights  of  hydrogen,  oxygen, 
and  sodium. 

This  will  give  you  a  rough  idea  of  Dalton's  theory  of 
atoms.  There  is  always  this  difficulty  in  it  that  we  cannot 
be  quite  sure  when  we  have  arrived  at  the  smallest  quantity 
of  any  substance  ;  for  suppose  that  one  day  we  were  to  find 
that  oxygen  could  be  split  up  into  two  substances,  then  it 
would  no  longer  be  true  that  an  atom  of  oxygen  could  not 
be  divided.  It  would  then  be  made  up  of  two  elements,  the 
smallest  quantities  of  which,  when  joined  together,  would 
weigh  16.  But  if  we  bear  this  possibility  in  mind,  then  the 
theory  is  of  great  use  in  giving  us  the  symbols  which  are  now 
used  in  chemical  language.  For  when  it  was  once  agreed 
that  the  weight  of  an  atom  of  hydrogen  should  be  reckoned 
as  I,  then  an  atom  of  oxygen  will  weigh  16,  and  the  letters 
HHO  express  a  great  deal.  They  tell  us  that  two  atoms  of 
hydrogen  weighing  2  are  joined  to  one  atom  of  oxygen  weigli- 
ing  16,  to   form  a  molecule  of  water.     In  the  same  way 


CH.  xxxvi.        LIEBIG— ORGANIC   CHEMISTRY.  377 

HOjNa^  tells  us  that  one  atom  of  each  of  these  substances, 
weighing  respectively,  i,  16,  23,  form  a  molecule  of  soda. 
And  thus  a  complete  chemical  language  has  sprung  up,  by 
which  chemists  in  all  parts  of  the  world  can  understand  at 
once  what  is  the  composition  of  any  substance;  and  by 
means  of  these  simple  letters  the  most  complicated  chemical 
problems  can  be  worked  out  clearly  and  intelligibly. 

Dalton's  theory  was  received  very  quickly  by  chemists, 
considering  how  entirely  new  the  ideas  were  which  it 
taught.  His  friend  Dr.  Thomson,  an  eminent  chemist 
(born  1773,  died  1852),  gave  a  very  clear  account  of  it  in 
his  '  System  of  Chemistry,'  and  brought  it  under  the  notice 
of  Davy  and  Faraday  ;  and  a  great  French  chemist,  Gay- 
Lussac  (born  1778,  died  1850),  adopted  it  at  once,  and 
added  another  discovery  in  favour  of  it  in  1809 — namely, 
that  when  substances  are  reduced  to  gas,  and  the  gas  is 
collected,  it  is  found  that  the  different  elements  combine  in 
equal  or  multiple  volumes. 

You  will  understand  this  by  turning  back  to  the  com- 
pounds of  nitrogen  and  oxygen  (p.  373),  where  you  will  see 
that  there  was  always  either  i,  2,  3,  4,  or  5  volumes  of 
oxygen  collected  for  one  of  nitrogen,  and  never  a  part 
of  a  volume.  This  was  really  a  different  fact  from  the  one 
Dalton  pointed  out,  that  the  elements  combine  in  definite 
weights,  and  it  was  necessary  to  complete  the  law  of  mul- 
tiple proportions. 

Liebig  the  Great  Teacher  in  Organic  Chemistry. — And 
now,  before  closing  the  history  of  chemistry,  we  must  mention, 
in  passing,  one  great  division  of  the  science  of  which  we 
cannot  attempt  to  give  any  real  account — namely,  the  science 

»  Na  stands  for  Natrium,  the  Latin  name  for  soda,  now  used  for 
the  metal  sodium. 


378  NINETEENTH  CENTURY.  pt.  hi. 

of  organic  chemistry^  or  the  chemistry  of  living  bodies.  This 
study  began,  as  you  will  remember,  when  Boerhaave  first 
examined  the  juices  of  plants  and  the  fluids  in  animal 
bodies.  But  it  can  scarcely  be  said  to  have  made  any  great 
advance  till  the  year  1828,  when  a  German  chemist  named 
Wohler  first  showed  that  urea,  a  substance  in  the  bodies 
of  animals,  can  be  made  artificially.  Since  then  Berthelot 
and  other  eminent  chemists  have  discovered  how  to  make 
many  compounds  in  the  laboratory  which  were  before  only 
found  in  living  beings. 

But  the  great  master  of  organic  chemistry  whose  name 
you  must  remember,  though  we  can  speak  but  little  about 
him,  was  Baron  Liebig,  of  Darmstadt,  who  was  born  in 
1803,  and  died  only  a  few  years  ago.  He  was  the  first  to 
analyse  organic  substances  satisfactorily,  by  heating  them  in 
vessels  with  metallic  oxides,  and  so  reducing  them  to  carbon 
and  their  other  elements ;  and  he  also  brought  agricultural 
chemistry  to  great  perfection.  This  subject,  which  was  first 
treated  by  Sir  H.  Davy,  teaches  how  the  grov/th  of  plants 
depends  upon  the  chemical  state  of  the  soil  in  which 
tliey  are  sown,  how  different  crops  should  be  sown  in  suc- 
cession in  any  field  so  as  not  to  exhaust  the  soil ;  and  what 
manure  will  best  give  back  to  the  ground  the  elements  which 
the  plants  have  taken  out  of  it.  Liebig  also  traced  out  the 
changes  which  food  undergoes  in  our  bodies,  and  studied 
which  kinds  turn  to  fat,  muscle,  blood,  or  sugar  in  our  system. 
In  1832  he  also  discovered  chloroform  and  chlorale,  though 
these  were  not  used  for  producing  unconsciousness  till  more 
than  fifteen  years  later  by  Dr.  Simpson. 

The  whole  history  of  organic  chemistry,  however,  is  far 
beyond  us  It  present  j  the  science  has  only  existed  for  the 
last  fifty  years,   and  the   chemical   substances  which   are 


4 

CH.  XXXVI.  ORGANIC   CHEMISTRY.  379 

created  in  a  living  body  are  extremely  complicated,  making 
the  whole  subject  very  difficult  to  understand.  Moreover, 
we  do  not  pretend  to  follow  out  the  particulars  of  any 
science ;  if  you  can  remember  the  names  of  some  of  the 
great  pioneers  of  chemistry  from  the  time  of  Geber  in  the 
ninth  century  up  to  the  days  of  Davy,  Faraday,  and  Liebig, 
and  have  some  slight  understanding  of  the  nature  of  the 
work  they  did,  it  is  all  we  can  attempt  in  a  book  of  this 
kind. 


Chief  Wo7'ks consulted.  —  Davy's  'Works,'  1840;  Whewell's  'Induc- 
tive Sciences;'  Dalton's  'Chemical  Philosophy,'  1808;  Dr.  Henry's 
'Memoir  ofDalton,'  1854;  Fownes's  'Chemistry;'  Brande's  'Che- 
mistry ; '  Faraday's  *  Various  Forces  of  Nature  ; '  '  Edinburgh  Re- 
view,'vol.  xciv.  '  Modem  Chemistry  ; '  Hoffmann,  'On  Liebig  and 
Faraday.' 


38o  NINETEENTH  CENTURY.  pt.  hi. 


CHAPTER    XXXVII. 

SCIENCE  OF  THE  NINETEENTH  CENTURY  (CONTINUED). 

The  Organic  Sciences  are  too  difficult  to  follow  out  in  detail — ^Jussieu's 
Natural  System  of  Plants — Goethe  proves  the  Metamorphosis  of 
Plants —  Humboldt  studies  the  Lines  of  average  Temperature  on  the 
Globe — Extends  our  knowledge  of  Physical  Geography — Writes  the 
'  Cosmos  '—Death  of  Humboldt  in  1858. 

The  short  sketch  of  advances  in  modern  chemistry  given  in 
the  last  chapter  brings  us  to  the  end  of  the  physical  sciences, 
or  those  which  deal  more  particularly  with  the  properties  of 
bodies,  and  the  laws  of  their  action  upon  each  other.  We 
must  now  pass  on  to  those  sciences  which  treat  of  the  past 
and  present  history  of  the  globe  and  the  living  beings  which 
inhabit  it.  I  shall  not  attempt  to  speak  of  these  sciences 
separately,  for  it  is  clearly  impossible  without  a  great  deal 
of  special  knowledge  to  follow  the  modern  discoveries  in 
physiology,  anatomy,  medicine,  zoology,  botany,  and  geology. 
All  these  sciences  had  advanced  rapidly  since  the  time 
of  Haller  and  Hunter,  Linnaeus  and  Buffon.  Famous 
anatomists  and  physiologists  such  as  the  two  Monros,  father 
and  son,  in  England,  Bichat  (17  71-1802)  in  France, 
Camper  (1722-1789)  and  Blumenbach  (1752-1840)  in  Ger- 
many, had  been  carrying  on  the  study  of  the  comparative 
structure  of  men  and  animals,  and  training  up  students  to 
understand,  far  more  completely  than  before,  the  functions 


cii.  XXXVII.  GOETHE  A   BOTANIST.  381 

of  living  beings.  And  the  followers  of  Linnaeus  all  over 
the  world  had  been  collecting  and  sending  home  for  com- 
parison rare  plants  and  animals  formerly  unknown,  which 
were  eagerly  studied  for  the  new  light  they  threw  upon  those 
which  had  been  already  dissected  and  described. 

And  so  it  came  to  pass  that  towards  the  end  of  the 
eighteenth  century  men  became  eager  not  merely  to  examine 
separate  specimens  or  structures,  but  to  form  theories  about 
the  living  beings  on  the  globe.  They  began  to  inquire  why 
animals  should  all  be  so  much  alike  in  their  general  plan, 
and  yet  so  different  in  their  special  characters  \  why  the 
same  part  of  the  body  should  be  made  to  serve  for  different 
purposes  in  different  animals,  instead  of  a  special  organ  being 
provided  ;  as,  for  example,  the  wing  of  the  bat,  which  answers 
exactly  to  the  front  leg  of  a  mouse,  but  is  altered  so  as  to 
be  used  for  flying  instead  of  walking.  Then  again,  as  the 
distribution  of  animals  became  better  known,  the  question 
arose  why  certain  kinds,  such  as  kangaroos,  should  be  found 
only  in  Australia,  while  they  are  wanting  in  all  other  parts 
of  the  world.  Such  general  questions  as  these  began  to 
occupy  the  minds  of  naturalists,  and  we  cannot  close  a 
history  of  science  without  trying  to  understand  something 
of  the  attempts  made  to  answer  them,  although  they  are 
so  difficult  that  it  will  require  all  your  attention  and 
thought  to  understand  them. 

The  Poet  Goethe  proves  the  Metamorphosis  or  Transfor- 
mation of  Plants,  1790. — One  of  the  first  men  who  threw 
any  light  upon  the  history  of  the  growth  of  plants  was  the 
poet  Goethe.  Goethe  had  a  deep  love  of  Nature,  as  may 
be  seen  in  many  of  his  beautiful  minor  poems,  and  this  love 
led  him  in  the  year  1780  to  devote  himself  to  the  study  of 
rhe  anatomy  of  plants  and  animals. 


382  NINETEENTH  CENTURY.  PT.  in. 

Since  the  time  of  Linnaeus  botany  had  become  very- 
popular,  and  the  two  celebrated  French  botanists,  Antoine 
de  Jussieu  and  his  son  Bernard  de  Jussieu,  had  established 
the  Natural  System  of  plants,  which  obliges  men  to  observe 
every  part  of  a  plant  before  placing  it  in  a  class  or  order. 
You  will  remember  that  Linnaeus  suggested  this  method  (see 
p.  2ii),  but  thought  it  too  difficult  for  ordinary  students,  and 
even  to  this  day  the  Artificial  System  of  Linnaeus  is  used 
side  by  side  with  Jussieu's. 

The  study  of  the  Natural  System,  however,  led  botan- 
ists to  observe  more  carefully  the  nature  of  plants  and  the 
manner  in  which  they  grow ;  and  when  Goethe  turned  his 
attention  to  botany  he  was  very  much  struck  with  the 
power  which  plants  have  of  transforming  or  changing 
the  growth  of  their  parts.  For  example,  the  common  wild 
rose  in  the  hedges  has  a  crown  of  pink  petals,  with  stamens 
and  pistils  in  the  centre;  but  the  garden  rose,  which  is 
nothing  more  than  the  wild  rose  grown  in  a  better  soil,  has 
lost  the  stamens  and  pistils,  or  rather  has  changed  them  into 
flower-leaves,  so  that  the  whole  flower  is  one  mass  of  petals, 
and  rarely  forms  any  seeds. 

It  is  clear,  therefore^  said  Goethe,  that  the  stamens  and 
pistil  of  a  plant  are  nothing  more  nor  less  than  flower-leaves 
transformed  into  a  peculiar  shape,  so  that  they  serve  to  form 
seeds,  and  to  carry  on  the  life  of  the  plant.  And  this  is 
true  of  all  the  different  parts  of  the  plants.  Wherever  you 
look  in  the  vegetable  kingdom,  you  will  find  that  every  part 
of  a  plant  is  nothing  more  than  stem  or  leaves  altered  in 
various  ways  to  suit  the  work  they  have  fo  do.  Thus  the 
stem  of  a  geranium,  the  trunk  of  a  tree,  the  twining  stalk 
of  the  vine,  the  straw  of  wheat,  the  thorns  of  a  rose-bush, 


CH.  x-xxvii.       THE  METAMORPHOSIS   OF  PLANTS.       383 

the  runners  of  a  strawberry,  the  roots  of  plants,  and  the 
fleshy  potato,  are  all  only  different  forms  of  stems  and 
branches.  Again,  the  two  cotyledons  of  a  seed  which  are 
well  seen  in  the  halves  of  a  bean  are  but  the  first  pair  of 
leaves.  Out  of  them  grows  the  stem,  and  out  of  this,  leaves 
of  different  forms  according  to  the  peculiar  species  of 
plant. 

Then,  as  the  plant  developes,  come  the  buds  of  the  flower, 
but  these  again  are  only  stems  and  leaves  growing  more 
thickly  together.  We  find  in  different  plants  every  variety 
of  flower  from  mere  green  leaf-like  blossoms  to  the  most 
gorgeous  colours.  The  green  leaves  called  sepals,  which 
lie  under  the  yellow  petals  in  the  buttercup,  are  transformed 
into  brilliantly  coloured  petals  in  the  tulip,  while  in  some 
cases,  such  as  occasionally  in  white  clover,  the  whole  flower, 
sepals,  petals,  pistil  and  stamens,  has  been  known  to  be 
changed  into  little  leaflets  growing  as  if  upon  a  branch. 

For  this  reason  gardeners  find  it  possible  to  cultivate  a 
plant  so  that  it  shall  be  all  leaves  and  no  flower,  or,  oi\  the 
other  hand,  shall  have  a  gorgeous  flower  while  the  leaves 
remain  small  and  insignificant ;  or,  as  in  the  potato  or  the 
turnip,  they  can  increase  the  size  of  the  root  at  the  expense 
of  the  leaves  and  flowers.  And  thus  we  are  led  to  see  that 
all  the  different  parts  of  a  plant  are  only  peculiar  transfor- 
mations of  simple  stems  and  leaves,  such  as  we  fin^  in 
mosses  and  the  lowest  forms  of  plants. 

This  beautiful  truth  of  the  transformation  or  metamor- 
phosis of  plants  we  owe  to  the  poet  Goethe ;  for  though 
Linnaeus  suggested  it  rather  vaguely  in  some  of  his  writings, 
and  a  botanist  named  Wolff  seems  also  to  have  taught  it, 
yet  it  was  Goethe's  essay  on  the  '  Metamorphosis  of  Plants,' 


384  NINETEENTH  CENTURY,  pt.  hi. 

published  in  1790,  which  first  led  naturalists  to  consider  the 
question.  Goethe's  work  was  very  little  read  at  first,  and 
he  had  great  difficulty  in  finding  a  publisher  for  it,  for  it  was 
thought  that  a  poet  could  not  know  much  of  science  ; 
but  the  great  Swiss  botanist,  Auguste  de  Candolle  (born 
1778,  died  1841)  seeing  what  a  new  hght  it  threw  upon  the 
study  of  plants,  taught  it  in  his  works,  and  then  it  became 
gradually  known  as  one  of  the  greatest  discoveries  in  modern 
botany. 

Alexander  von  Humboldt  studies  the  Lines  of  Equal 
Heat  over  the  Globe— Founds  the  Study  of  Physical  Geo- 
graphy—Writes the  <  Cosmos,'  1793-1859.— While  Goethe 
was  studying  plants  at  Weimar,  and  learning  the  secrets  of 
Nature  in  the  quiet  of  his  own  home,  another  man  of  whom 
we  must  now  speak,  was  planning  to  travel  in  distant 
countries,  and  to  write  a  history,  as  far  as  he  was  able,  of 
the  work  which  Nature  is  doing  all  over  the  world. 

Alexander  von  Humboldt,  who  forms  a  link  between  the 
science  of  the  eighteenth  and  the  nineteenth  centuries,  was 
born  at  Berlin  in  1769,  and  was  educated  (together  with 
his  brother  William,  the  great  politician)  at  the  University 
of  Gottingen.  At  the  age  of  one-and-twenty  he  went  to 
Freyberg,  where  he  was  a  pupil  of  Werner.  It  was  at  this 
time,  when  he  was  only  just  of  age,  that  he  formed  the  plan 
in  his  mind  of  spending  his  life  in  studying  the  works  of 
Nature,  and  writing  a  '  grand  and  general  view  of  the  Uni- 
verse.' 

The  first  sketch  of  his  book,  which  he  called  '  Cosmos,' 
or  'The  Universe,'  was  written  in  1793,  when  he  was  only 
twenty-four;  and  the  last  sheets  were  printed  in  1859,  when 
he  was  ninety  years  of  age.  In  the  sixty-six  years  between 
these   two  dates    he   collected   and   published   in  popular 


cii.  XXXVII.  HUMBOLDTS   TRA  VELS,  385 

language  an  immense  number  of  facts  about  nature  in  all 
parts  of  the  world. 

His  chief  voyage  was  to  America  in  1799,  when  he  spent 
six  years  in  Mexico,  and  along  the  shores  of  the  Orinoco. 
Here  he  began  one  of  his  greatest  undertakings,  namely 
finding  out  the  climate  of  different  parts  of  the  world,  and 
tracing  out  isothermal  lines,  or  lines  of  equal  heat  over  the 
globe,   showing  what   countries   have    the    same    average 
temperature,   and   explaining   why  some  enjoy  an   almost 
equable  climate  all  the  year  round,  while  others  are  very  hot 
in  summer  and  cold  in  winter.     For  example,  he  pointed 
out  that  Greenland  is  much  colder  than  Lapland,  even  in 
places  which  are  on  the  same  line  of  latitude,  because  a 
cold   current   from   the  North  Pole  flows  past  Greenland, 
while  the  warm  Gulf  Stream  crosses  over  from  the  Gulf  of 
Mexico  and  washes  the  shores  of  Lapland.     The  import- 
ance of  this  study  of  variations  of  temperature  was  first 
pointed  out  by  Humboldt,  and  it  should  be  remembered 
as  one  of  his  most  original  investigations. 

Again,  in  his  long  journeys  through  South  America,  he 
traced  everywhere  the  different  species  of  plants  which 
grew  at  various  heights,  even  up  to  20,000  feet  on  the  slopes 
of  the  Andes.  This  led  him  to  try  and  find  the  reasons 
why  certain  plants  are  only  to  be  found  in  certain  areas,  in 
the  same  way  that  Buffon  had  worked  out  the  distribution  ot 
animals.  When  he  returned  to  Paris  in  1804  he  had  col- 
lected an  immense  number  of  facts  as  to  the  heights  of 
mountains,  the  climate  of  countries,  the  minerals  and  metals 
found  in  them,  the  active  and  extinct  volcanoes,  the  nature 
of  the  rocks  and  soils,  the  vegetation  and  the  animals  ;  and 
with  the  help  of  the  best  scientific  men  in  Paris   (each 

18 


386  NINETEENTH  CENTURY,  rx.  in. 


undertaking  his  own  special  science)  he  published  twenty- 
eight  large  volumes,  which  contained  the  conclusions  based 
upon  the  facts  he  had  learnt  in  his  travels. 

In  1827  he  returned  to  Berlin,  and  was  then  invited  by 
the  Emperor  of  Russia  to  go  on  a  journey  into  the  Russian 
provinces  of  Asia,  where  he  spent  nine  months  making  the 
same  kind  of  observations  that  he  had  made  in  America. 
In  1830  he  was  sent  to  Paris  as  Prussian  ambassador,  and 
it  was  not  till  he  returned  to  Berlin  some  years  after,  that 
he  began  to  publish  the  '  Cosmos  '  he  had  been  preparing 
for  so  long. 

In  this  grand  work  he  gives  a  complete  history  of 
astronomy,  and  all  the  discoveries  in  it  made  up  till  his 
time ;  and  then  taking  our  own  world  as  part  of  the  uni- 
verse, he  describes  the  changes  which  are  going  on  now,  or 
have  been  going  on  in  past  time,  on  the  face  of  the  earth. 
It  is  to  Humboldt  that  we  owe  much  which  makes  geo- 
graphy interesting.  The  study  of  the  surface  of  the  globe, 
of  mountain-chains,  table-lands,  and  rivers,  the  climates  of 
countries,  the  different  winds  which  blow,  and  the  currents 
which  cross  the  ocean ;  the  way  in  which  plants  and  ani- 
mals are  distributed  over  the  world  \  the  different  races  of 
men,  and  how  they  have  spread  over  the  globe — all  these 
and  other  facts  which  make  geography  something  more  than 
a  mere  list  of  names,  Humboldt  studied  during  his  various 
journeys,  and  related  them  with  a  freshness  which  °had  a 
peculiar  charm. 

It  was  not  so  much  that  he  advanced  any  one  branch 
of  science  as  that  he  led  men  to  look  upon  the  earth  and  the 
universe  as  one  vast  whole,  and  to  find  a  living  interest  in 
every  part  of  it.  In  1858  the  last  sheets  of  the  'Cosmos' 
were  put  into  the  publisher's  hands,  but  Humboldt  did  not 


CH.  XXXVII.  DEA  TH  OF  HUMBOLDT.  387 

live  to  see  them  finished.  He  had  done  his  part :  the  work 
he  had  proposed  to  himself  was  completed,  and  he  fell 
peacefully  asleep  on  the  6th  of  May,  1859. 


Chief  Works  consulted. — Goethe's  *  CEuvres  Scientifiques  ;'  Faivre  ; 
Asa  Gray's  *  Botany ; '  L.  Agassiz's  '  Centenary  Address  on  A.  von 
Humboldt ; '  Humboldt's  *  Cosmos. ' 


NINETEENTH  CENTURY.  pt.  hi. 


CHAPTER   XXXVIII. 

SCIENCE  OF  THE  NINETEENTH  CENTURY  (CONTINUED). 

The  three  Naturalists,  Lamarck,  Cuvier,  and  Geoffroy  St.-Hilaire — 
Cuvier  begins  the  Museum  of  Comparative  Anatomy — Lamarck's  . 
History  of  Invertebrate  Animals — Geoffroy  St.-Hilaire  brings  Natural 
History  Collections  from  Egypt — Lamarck  on  the  Development  of 
Animals — Geoffroy  St.-Hilaire  on  *  Homology,'  or  the  similarity  in 
the  parts  of  different  Animals — Cuvier's  *Regne  Animal,'  and  his 
Classification  of  Animals — Cuvier  on  the  perfect  agreement  between 
the  different  parts  of  an  Animal — He  studies  and  restores  the  re- 
mains of  Fossil  Animals — His  *  Ossemens  Fossiles ' — Death  of 
Cuvier — Von  Baer  on  the  study  of  Embryology — His  History  of  the 
Development  of  Animals,  1828. 

Lamarck — Cuvier — St.-Hilaire. — When  Humboldt  visited 
Paris  in  1804  there  were  three  men  holding  professorships  j 
in  the  Museum  of  Natural  History  in  that  city,  who  had  \ 
afterwards  a  great  influence  upon  the  study  of  the  science  j 
of  living  beings.  These  three  men  were  Lamarck,  pro-  j 
fessor  of  zoology ;  Geoffroy  St.-Hilaire,  his  fellow-professor ; 
and  Cuvier,  assistant-professor  of  comparative  anatomy. 

The  early  part  of  the  nineteenth  century  was,  as  you 
will  remember,  a  very  troubled  time  for  France.  The  first 
Napoleon  was  carrying  war  and  desolation  all  over  Europe, 
and  Paris  was  kept  in  a  constant  state  of  turmoil  for  many 
years.  During  all  this  time  it  is  interesting  to  see  how 
steadily  and  quietly  the  three  men  I  have  mentioned  pur- 
sued their  search  after  knowledge.     Geoffroy   St.-Hilaire 


CH.  XXXVIII.  LAMARCK— CUVIER.  389 

twice  risked  his  life  in  saving  friends  from  the  terrors  of  the 

Revolution;   and  Cuvier  held  political  appointments  both 

under  Napoleon  and  under  Louis  Phihppe  ;  but  in  spite  of 

these    duties  and    interruptions   their   scientific   work   was 

never  neglected ;  and  a  great  part  of  the  knowledge  about 

plants  and  animals  which  we  now  possess  was  accumulated 

during  the  troublous  times  of  the  French  revolutions. 

Jean   Baptiste   de  Monet,  Chevalier   de  Lamarck,  the 

elder  of  these  three  men,  was  born  in  1 744  at  Bezantin,  in 

Picardy,  and  a  somewhat  curious  circumstance  led  him  to 

devote  his  life  to  science.     His  father  intended  him  for  the 

church,  but  the  lad  had  a  passion  for  the  army,  and  on  his 
» 
father's  death,  in  1760,  set  off  to  Germany,  where  the  French 

were  then  fighting,  and  soon  distinguished  himself  as  a  volun- 
teer. Some  time  afterwards,  however,  one  of  his  comrades 
lifted  him  up  by  his  head  in  joke,  and  so  strained  the  glands 
of  the  neck  that  after  a  very  severe  illness  he  was  obliged  to 
give  up  his  profession  and  become  a  banker's  clerk  in  Paris. 
He  had  thus  time  and  opportunity  to  study  natural  science, 
for  which  he  had  always  had  a  great  liking,  and  in  1778  he 
published  a  small  book  on  botany.  Buffon,  who  was  then 
at  the  height  of  his  fame,  was  pleased  with  this  work,  and 
procured  for  Lamarck  an  appointment  in  the  botanical  de- 
partment of  the  Academic  des  Sciences.  From  there  he 
went  to  the  Jardin  des  Plantes,  and  eventually  became  pro- 
fessor of  geology  in  the  Musee  d'Histoire  Naturelle. 

George  Leopold  Cuvier,  afterwards  made  Baron  Cuvier  by 
Louis  XVIIL,  was  bom  of  Swiss  parents  at  Montbeliard,  near 
Besangon,  in  1769.  He,  too,  was  intended  for  the  church, 
because  his  parents  were  not  rich  and  he  had  an  uncle  who 
could  help  him  in  that  profession  ;  but  Prince  Charles  of 
Wurtemberg  having  heard  of  his  abilities,  sent  for  him  and 


390  NINETEENTH  CENTURY.  pt.  hi. 

gave  him  a  free  education  in  the  Acadeinie  Caroline  at  the 
University  of  Stuttgard.  Here  he  already  began  in  his  spare 
moments  to  read  books  of  natural  history  and  make  drawings 
of  plants  and  animals.  When  he  left  Stuttgard  he  went  as 
tutor  in  a  nobleman's  family  at  Caen,  in  Normandy,  and  found 
a  new  and  delightful  study  in  the  examination  of  the  marine 
animals  on  the  sea-shore.  After  living  there  six  years,  he 
happened  to  meet  the  celebrated  Abbe  Tessier,  who  had  fled 
from  the  Revolution  in  Paris,  and  through  his  means  the  young 
Cuvier  was  introduced  to  Geoffroy  St.-Hilaire  and  other 
scientific  men  in  Paris,  and  became  assistant-professor  of 
comparative  anatomy  in  the  Jardin  des  Plantes.  From  this 
post  he  rose  to  very  great  honours  both  as  a  politician  and 
man  of  science,  holding  the  posts  of  President  of  the  In- 
stitute, Inspector- General  of  Education,  Councillor  of  the 
Imperial  University,  and  many  others  of  equal  importance. 

Geoffroy  St.-Hilaire,  the  third  and  youngest  of  the  three 
friends,  was  born  at  Etampes  in  1772.  It  is  curious  that  he 
also  began  his  education  as  a  priest,  and  that  all  these 
three  men  should  have  given  up  the  church  for  science. 
In  St.-Hilaire's  case  it  was  a  passionate  love  for  zoology 
which  led  him  to  persuade  his  father  to  let  him  stop  in  Paris 
to  study  at  the  Jardin  des  Plantes,  where  he  was  soon 
offered  a  post  which  gave  him  an  excuse  for  following  his 
own  tastes.  He  afterwards  joined  Lamarck  at  the  Musee 
d'Histoire  Naturelle  in  1793  ;  and  in  1795  it  was  chiefly 
through  his  influence  that  Cuvier  was  invited  to  Paris  and 
became  their  fellow-worker. 

It  now  remains  for  us  to  see  what  was  done  by  these 
three  remarkable  men.  For  three  years  they  all  remained  at 
work  in  the  museum.  Cuvier  had  found  in  a  lumber-room 
four  or  five  old  skeletons  collected  by  Daubenton  (p.  205), 


CH.  XXXVIII.     DEVELOPMENT  OF  ANIMALS.  391 

and  he  determined  to  make  them  the  beginning  of  a  mu- 
seum of  comparative  anatomy,  which  afterwards  became 
very  famous.  St.-Hilaire  worked  with  Cuvier,  while  Lamarck 
began  the  study  of  those  animals — such  as  insects,  snails," 
worms,  shell-fish,  sea-anemones,  and  sponges — which  have 
no  backbone,  and  to  which  he  first  gave  the  name  of  '  in- 
vertebrate animals.'  Lamarck's  work  on  these  animals  is 
one  of  the  most  famous  he  ever  wrote. 

In  1798  Cuvier  and  St.-Hiliare  were  both  invited  by 
Napoleon  I.  to  go  with  the  French  army  to  Egypt  and 
study  the  curiosities  of  natural  history  which  were  to  be 
found  there.  Cuvier  declined,  but  St.-Hilaire  went,  and 
spent  three  years  examining  the  embalmed  animals  of  the 
Egyptians.  He  succeeded  in  1801  in  bringing  away  the 
beautiful  collections  of  these  and  other  relics  from  Alexan- 
dria, when  the  French  were  forced  to  give  up  the  town  to 
the  English.  These  collections  were  conveyed  safely  to  the 
Museum  in  Paris  in  1802. 

Lamarck  on  the  Development  of  Animals,  1801. — Mean- 
while Lamarck  published  in  1801  a  little  work  on  the 
'  Organization  of  Living  Bodies,'  and  in  it  he  first  suggested 
that  the  different  animals  were  not  created  separately,  but 
had  been  gradually  altered  from  a  few  simple  living  forms, 
so  that,  in  the  course  of  long  ages,  there  had  sprung  up  an 
immense  variety  of  species  of  animals  in  the  world.  It  must 
be  remembered  that  Lamarc!^  had  chiefly  studied  plants  and 
the  lower  animals.  We  have  seen  how  Goethe  showed  that 
all  plants  are  only  altered  stems  and  leaves  \  and  the  lower 
animals,  such  as  jelly-fish,  snails,  and  worms,  differ  much 
less  from  each  other  than  the  higher  animals  do.  There- 
fore Lamarck  was  very  much  struck  with  the  difficulty  there 
was  in  settling  which  were  distinct  forms  or  species,  and 


392  NINETEENTH  CENTURY.  pt.  hi. 

which  might  have  come  from  the  same  parent,  and  he  con- 
cluded that  the  only  difference  was  that  some  had  branched 
off  from  the  common  stock  earlier  than  others,  and  so  had 
become  rnore  unlike — ^just  as  brothers  and  sisters  are  very 
like  each  other  while  distant  cousins  are  much  less  liable  to 
have  the  same  features  and  expression. 

The  more  we  know  of  animals  and  plants,  said  La- 
marck, the  more  difficult  we  find  it  to  settle  which  are 
related  to  each  other  and  which  are  not.  Linnaeus  had  long 
ago  pointed  out  that  among  plants  which  are  well  known, 
such  as  the  willows  in  Europe,  the  cactuses  in  South 
America,  and  the  heaths  and  everlastings  at  the  Cape,  there 
are  so  many  kinds  differing  very  little  from  each  other  that  it 
is  impossible  to  say  which  ought  to  be  considered  as  separate 
species  and  which  as  the  descendants  of  one  kind  of  plant. 

Moreover,  we  know  how  much  plants  and  animals  are 
sometimes  altered  even  in  a  few  years.  For  example,  by 
growing  in  a  drier  soil  or  up  a  high  mountain,  plants 
become  stunted  and  altered  in  many  ways,  while  birds  when 
shut  up  lose  the  power  of  using  their  wings,  as  has  been  the 
case  with  our  domestic  poultry.  Man  can  make  a  number 
of  different  varieties  both  of  plants  and  animals  by  merely 
keeping  those  which  have  the  peculiarities  he  admires.  The 
different  kinds  of  pigeon,  for  example — the  pouters,  fan-tails, 
tumblers,  and  others,  which  are  so  unlike  each  other— are 
said  by  naturalists  to  be  all  descendants  of  the  common 
rock-pigeon  ;  and  all  the  varieties  of  rabbit  have  come  from 
one  wild  species.  You  cannot  find  a  wild  pigeon  with  a 
fan-tail,  or  a  wild  rabbit  with  lop-ears. 

If  man,  then,  in  a  few  hundred  years  can  make  such 
changes,  '  is  it  not  possible,'  said  Lamarck,  '  that  nature  in 
all  the  long  ages  during  which  the  world  has  existed,  may 


CH.  xxxvni.      MODIFICATION  OF  ORGANS.  393 

have  produced  the  different  kinds  of  plants  and  animals  by 
gradually  enlarging  one  part  and  diminishing  another  to  suit 
the  wants  of  each  ? '  These  and  many  other  arguments 
Lamarck  brought  forward  in  his  work  in  1801,  and  again  in 
his  '  Philosophie  Zoologique  '  in  1809,  to  prove  that  the  way 
in  which  the  Creator  has  formed  different  plants  and  animals 
has  been  by  altering  them  gradually  out  of  simple  forms. 

There  was,  however,  one  very  weak  point  in  all  his  cugu- 
ments  ;  he  did  not  show  sufficiently  what  should  cause  living 
beings  to  go  on  altering,  and  becoming  more  and  more  dif- 
ferent. For  if'  you  turn  plants  and  animals,  which  man  has 
altered,  out  into  the  fields  again,  in  a  very  few  generations 
they  return  very  nearly  to  their  old  forms  ;  nor  can  we  see 
any  reason  why  the  differences  between  animals  should  go 
on  increasing  unless  they  were  picked  out  and  kept  apart, 
as  men  keep  them  when  they  want  to  get  new  varieties. 

Lamarck  did,  indeed,  point  out  that  climate  and  dif- 
ference of  food  would  help  to  alter  the  nature  of  an  animal, 
but  the  chief  reason  he  gave  for  changes  taking  place  in 
them,  was  that  the  animal  itself  might  cause  the  alteration  in 
its  form  3  as  for  instance,  a  giraffe  constantly  wishing  to  eat  the 
boughs  off  high  trees  might  stretch  his  neck,  and  so  by  de- 
grees each  generation  might  have  longer  necks  than  the  last 
one.  This  reason  was  so  weak  and  ridiculous  that  it  prevented 
naturalists  from  paying  much  attention  to  Lamarck's  theory. 

Geoffroy  St.-Hilaire  points  out  that  the  Parts  or 
Organs  are  the  same  in  all  Animals,  only  Modified  to 
suit  their  Wants. — Nevertheless  Geoffroy  St.-Hilaire  was 
inclined  to  think  there  was  some  truth  in  this  theory,  although 
Cuvier  was  strongly  against  it.  Cuvier,  you  remember,  had 
given  his  time  chiefly  to  the  restoration  of  the  skeletons  of 
the  higher  animals,  and  he  was  as  much  struck  with  the  im- 


394  •  NINETEENTH  CENTURY.  pt.  iir. 

mense  difference  between  them,  as  Lamarck  had  been  with 
the  Hkeness  of  the  lower  animals.  Cuvier  thought  that  each 
animal  was  at  first  created  separately,  and  all  its  parts  were 
arranged  expressly  to  meet  its  wants.  He  looked  upon  the 
creation  of  each  kind  of  animal  as  the  making  of  a  machine, 
where  we  put  a  wheel  here  and  a  valve  there  expressly  to 
make  it  do  the  work  required. 

Geoffroy  St.-Hilaire,  on  the  contrary,  insisted  that  we 
never  find  any  part  of  an  animal  which  we  can  say  was  made 
expressly  for  it.  Whenever  we  examine  it  closely  enough 
we  find  it  is  exactly  the  same  as  exists  in  other  beings,  only 
its  growth  is  altered  so  as  to  make  it  useful  to  that  particular 
animal.  The  pouch  of  the  Kangaroo,  he  said,  is  only  a  fold 
of  the  skin  which  is  looser  than  in  other  animals  ;  the  trimk 
of  the  elephant  is  a  nose  which  has  become  extremely  long ; 
the  hand  of  a  man,  the  leg  of  a  horse,  and  the  wing  of  a 
bat,  are  the  same  organ  and  have  the  same  bones,  although 
they  serve  such  different  purposes.  '  Nature,'  he  said, '  has 
formed  all  living  beings  on  one  plan,  essentially  the  same  in 
principle,  but  varied  in  a  thousand  ways  in  all  the  minor 
parts  j  all  the  differences  are  only  a  complication  and 
modification  of  the  same  organs.' 

This  similarity  of  structure,  or  homology  as  it  is  called, 
which  runs  through  all  animals,  was  thus  first  clearly  stated 
by  St.-Hilaire,  and  it  has  now  been  most  carefully  worked 
out  and  confirmed  by  our  living  anatomists.  Yet  Cuvier  op- 
posed it  to  the  last,  for  his  mind  was  full,  as  we  shall  see 
presently,  of  another  idea  which  is  equally  true  ;  namely,  how 
perfectly  each  part  of  an  animal  is  made  to  fit  all  the  other 
parts  of  his  body  ;  and  it  seemed  to  him  impossible  that  this 
could  be,  unless  each  part  was  created  expressly  for  the  work 
it  had  to  do. 


CH.  XXX.VIII.  CUVIERS   VIEWS.  395 

The  discussion  between  the  two  friends  became  so 
animated  that  all  Europe  was  excited  by  it.  It  is  said  that 
Goethe,  then  an  old  man  of  seventy-one,  meeting  a  friend, 
exclaimed,  '  Well  what  do  you  think  of  this  great  event  ?  the 
volcano  has  burst  forth,  all  is  in  flames.'  His  friend  thought 
he  spoke  of  the  French  Revolution,  and  answered  ac- 
cordingly. '  You  do  not  understand  me,'  said  Goethe,  '  I 
speak  of  the  discussion  between  Cuvier  and  St.-Hilaire:  the 
matter  is  of  the  highest  importance.  The  method  of  looking 
at  nature  which  St.-Hilaire  has  introduced  can  never  now  be 
lost  sight  of  again.'  And  he  was  right,  for  the  doctrine  of 
homology,  as  taught  by  St.-Hilaire,  is  one  of  the  strongest 
arguments  for  the  theory  of  the  development  of  living 
beings,  now  held  by  all  the  most  able  naturalists,  and  of 
which  we  shall  speak  in  Chapter  XL. 

Cuvier  proves  that  the  Parts  of  an  Animal  agree  so 
exactly  that  from  seeing  one  Fragment  the  Whole  can  be 
known. — We  have  seen  that  Cuvier  did  not  agree  with 
many  of  the  views  of  Lamarck  and  St.-Hilaire.  We  must 
now  consider  what  work  he  did  himself ;  for  though  all  the 
three  friends  laboured  well,  Cuvier  accomplished  the  most  of 
all.  He  had  a  most  remarkable  capacity  for  work  ;  we  find 
him  at  the  same  time  restoring  skeletons  and  studying  each 
bone  with  minute  care,  lecturing  to  large  bodies  of  students, 
writing  the  history  of  all  the  sciences,  and  examining  fossils 
from  the  rocks  ;  besides  presiding  over  councils  and  superin- 
tending national  education.  And  whatever  he  touched  was 
done  thoroughly  and  with  a  master-hand. 

His  first  great  work  was  to  collect  all  the  different  facts 
of  comparative  anatomy  established  since  the  time  of 
Hunter,  and,  adding  a  great  mass  of  his  own  observations,  to 
build  them  up  into  one  complete  science  of  anatomy.     In 


396  NINETEENTH  CENTURY.  pt.  hi. 

his  'Regne  Animal/  published  in  1817,  he  made  a  new 
classification  of  the  whole  animal  kingdom,  dividing  them 
into  four  great  branches.  The  vertehrata,  or  animals  with 
back-bones ;  the  molhisca,  or  soft-bodied  animals,  such  as 
snails ;  the  arttatlata,  or  animals,  such  as  crabs,  spiders,  bees, 
and  ants,  whose  bodies  are  composed  of  movable  parts, 
hardest  outside,  and  jointed  or  articulated  together ;  and 
the  radiata,  or  animals  whose  parts  are  arranged  round  an 
axis,  such  as  star-fish  and  polyps.  These  four  branches 
he  divided  again  •  into  classes,  orders,  families,  genera,  and 
species,  making  a  much  more  complete  classification  than 
Linnseus  had  done,  because  it  was  founded  more  upon  the 
internal  structure  of  animals. 

In  this  work  he  pointed  out  that  the  parts  of  an  animal 
are  made  to  fit  to  each  in  such  a  wonderful  manner,  that 
if  only  a  few  bones  are  placed  in  the  hands  of  an  ana- 
tomist he  ought  to  be  able  to  tell  you  exactly  what  all  the 
other  bones  must  be.  You  will  remember  that  Hunter 
had  hinted  at  this  when  he  showed  how  the  teeth  of  each 
species  of  animal  are  fitted  to  the  kind  of  stomach  into 
which  the  food  is  to  pass.  But  Cuvier  proved  that  this  is 
true  not  only  of  the  teeth  but  of  every  bone  in  the  skeleton 
of  an  animal. 

'  Every  organized  being,'  he  says,  '  forms  a  whole  and 
entire  system  .  .  .  none  of  its  parts  can  change  without  a 
change  of  the  others  also.  Thus,  if  the  stomach  of  an 
animal  is  made  so  as  only  to  digest  fresh  flesh,  his  jaws 
must  be  formed  to  devour  the  prey,  his  claws  to  seize  and 
tear  it,  his  teeth  to  divide  the  flesh,  and  the  whole  system  of 
his  organs  of  motion  to  follow  and  overtake  it.  Nature 
must  even  have  planted  in  his  brain  the  necessary  instinct  to 
hide  himself  and  lay  snares  for  his  victim.     These  are  the 


CH.  XXXVIII.     CUVIER  ON  FOSSIL  ANIMALS.  397 

general  conditions  of  a  carnivorous  life,  and  all  animals  who 
are  to  live  this  life  must  fulfil  them,  otherwise  they  cannot 
exist.  And  besides  these  general  conditions  there  are 
special  ones,  according  to  the  particular  kind  of  life  the 
animal  has  to  live,  and  each  of  these  require  modifications 
in  the  form  of  the  organs ;  so  that  not  only  the  class,  but  the 
order,  the  genus,  and  even  the  species  of  an  animal  are 
revealed  by  each  part  of  it.' 

And  now  you  will  understand  why  Cuvier  could  not 
believe  St.-Hilaire's  theory  that  all  the  parts  of  one  class  of 
animals— such  as  the  vertebrate  animals,  for  example— are 
made  on  one  model,  and  that  when  some  organ  has  to  play 
a  different  part  it  is  altered,  and  not  created  for  the  purpose. 
Cuvier  was  strongly  impressed  with  the  beautiful  agreement 
in  every  part  of  each  particular  animal,  which  enables  it  to 
provide  for  all  its  wants  ;  while  St.-Hilaire  was  equally  im- 
pressed with  the  general  agreement  between  the  structure  of 
all  animals  in  any  one  great  class.  Both  these  views  were 
true,  but  in  the  state  of  knowledge  at  that  time  it  was  very 
difficult  to  reconcile  them.  You  must  bear  this  in  mind, 
because  it  is  one  of  the  difliculties  upon  which  light  is  thrown 
by  Mr.  Darwin's  observations,  which  we  shall  examine 
by-and-by. 

Cuvier  Studies  and  Restores  the  Remains  of  Fossil 
Animals,  1812- — We  have  seen  that  Cuvier's  knowledge  of 
the  agreement  between  the  different  parts  of  an  animal  was 
so  great  that  from  even  one  bone  he  could  tell  what  the  other 
parts  of  the  body  must  be.  The  use  which  he  made  of  this 
knowledge  enabled  him  to  reveal  a  wonderful  history  about 
the  fossils  buried  in  the  crust  of  our  earth. 

When  he  first  came  to  Paris,  and  for  many  years  after- 
wards, a  number  of  skeletons  and  parts  of  skeletons  of  ani- 


39S  NINETEENTH  CENTURY.  pt.  hi. 

mals,  were  being  dug  up  round  about  Paris.  These  were  a 
great  puzzle  to  anatomists,  for  the  bones  were  many  of  them 
immensely  large,  and  none  of  them  seemed  to  agree  exactly 
with  those  of  any  known  animals.  Cuvier  no  sooner  heard 
of  these  fossils  than  he  set  to  work  to  study  them,  making 
use  of  his  great  knowledge  of  anatomy  to  sort  out  the  con- 
fused mass.  His  practised  eye  could  detect  from  among 
the  heap  of  bones  those  which  belonged  to  each  other,  and 
out  of  a  mere  handful  of  fragments  he  could  restore  in 
imagination  the  animal  from  which  they  must  have  come. 
It  was  like  the  work  of  an  enchanter's  wand. 

'  At  the  voice  of  comparative  anatomy,'  he  writes,  '  each 
bone,  each  fragment,  regained  its  place.  I  cannot  describe 
the  pleasure  I  felt  in  finding  that,  as  I  discovered  one  cha- 
racter, all  its  consequences  were  gradually  brought  to  light ; 
the  feet  agreed  with  the  history  told  by  the  teeth;  the  bones 
of  the  legs  and  thighs,  and  those  parts  which  ought  to  unite 
them,  agreed  with  each  other.  In  a  word,  each  one  of  the 
species  sprang  from  its  own  fragments.' 

And  so  month  after  month  he  worked  on,  and  then  to 
the  great  astonishment  of  naturalists  he  told  them  that 
all  these  animals  were  of  species  which  are  found  nowhere 
upon  the  earth  now.  They  were  all  extinct  animals.  The 
greater  part  belonged  to  hoofed  quadrupeds,  something 
like  our  elephant,  rhinoceros,  and  pig  j  then,  there  was  an 
elegant  deer-like  animal  resembling  a  gazelle,  some  birds, 
some  fish,  and  a  kind  of  opossum,  but  all  these  were  in 
some  way  different  from  any  which  live  now. 

Here  was  a  history  so  strange  that  at  first  no  one  would 
believe  it;  for  it  meant  that  at  the  time  when  the  land  on  which 
Paris  now  stands  was  being  laid  down  by  the  rivers,  there 
must  have  existed  a  whole  group  of  animals,  all  of  them 


CH.  XXXVIII.         LES  OSSEMENS  FOSSILES.  399 

more  or  less  different  from  our  present  species  of  animals, 
which  had  not  then  begun  to  exist.  It  had  long  been 
known  that  strange  shells  were  found  buried  in  the  earth's 
crust,  but  then  naturalists  could  never  be  sure  that  some 
like  them  might  not  be  living  in  other  parts  of  the  world 
without  our  knowing  it,  and  they  had  always  believed 
that  at  least  the  larger  animals  had  been  created .  quite 
recently  at  the  same  time  as  man.  But  here  were  ani- 
mals which  no  one  had  ever  seen  upon  the  earth,  and 
it  was  impossible  to  suppose  that  fifty  different  kinds  of 
creatures  of  all  sizes,  some  bigger  than  an  elephant,  could  be 
roaming  about  the  world  unseen  by  anyone.  Therefore 
there  could  be  no  doubt  that  long  before  the  time  of  history 
or  tradition  strange  animals  must  have  lived  and  died,  and 
have  been  buried  in  the  deposits  now  forming  part  of  the 
earth's  crust. 

And  when  this  was  once  recognised,  and  attention  was 
called  to  these  buried  animals,  little  by  little  other  forms 
were  found  in  older  rocks  in  different  parts  of  the  world, 
which  appeared  to  be  less  and  less  like  living  animals  the 
older  the  rocks  were  in  which  they  were  found.  All  these 
Cuvier  described  in  his  famous  work  called  *  Les  Ossemens 
Fossiles,'  which  he  published  in  18 12,  and  in  which  he  laid 
before  the  world  a  startling  history  of  the  long  succession  of 
different  animals  which  must  have  lived  in  past  ages  upon 
the  earth. 

'  And  here  we  must  close  this  very  imperfect  sketch  of  the 
work  done  by  the  three  French  naturalists.  You  ought 
chiefly  to  remember  about  them  that  Lamarck  suggested 
that  animals  have  been  developed  out  of  a  few  simple  forms; 
that  St.-Hilaire  proved  that  animals  of  one  class  are 
formed  on  the  same  general  plan,  similar  parts  being  altered 


400  NINETEENTH  CENTURY.  pt.  hi. 

to  serve  different  purposes  in  different  animals;  and  that 
Cuvier  showed  that  each  part  of  an  animal  agrees  with  the 
rest  so  perfectly  that  from  a  i^\f  bones  it  is  possible  to  tell 
exactly  what  animals  had  lived  and  died  in  past  ages. 

Geoffroy  St-.Hilaire  outlived  both  his  friends,  and  died  in 
1840.  Lamarck  had  died  in  1829,  in  his  eighty- fifth  year, 
having  been  blind  for  many  years.  Cuvier  died  on  May  13, 
1832.  On  the  Tuesday  previous  he  had  begun  his  third  course 
of  lectures  on  Natural  Science  at  the  College  de  France,  and 
had  promised  to  give  in  that  course  his  idea  of  creation,  and 
how  the  Divine  Intelligence  is  to  be  traced  through  all  the 
operations  of  nature  j  but  the  promise  remained  unfulfilled  ; 
that  same  evening  paralysis  set  in,  and  on  the  next  Sunday 
he  died  in  his  arm-chair  as  if  he  had  fallen  asleep.  He  had 
begged  to  be  buried  privately,  but  that  was  impossible  ;  on 
hearing  of  his  death  men  of  science  flocked  from  all  parts  to 
do  him  the  last  honour,  and  his  pupils  bore  him  to  the  grave. 

Von  Baer,  the  Founder  of  the  Study  of  Embryology. 
1828. — We  must  not  leave  this  question  of  the  structure  of 
animals  without  noticing  in  passing  a  new  and  important  study 
which  began  about  this  time.  This  was  the  study  of  embryo- 
logy, or  of  animals  in  the  earliest  stages  of  their  life,  as  in  the 
case  of  the  chicken  before  it  leaves  the  egg.  You  know  that 
if  you  take  a  bird's  &gg  when  it  is  newly  laid,  you  will  see 
inside  it  a  yellow  yolk  floating  in  a  white  fluid.  But  if  you 
take  the  egg  after  the  mother-bird  has  sat  upon  it  for  some 
days,  the  yolk  will  begin  to  have  the  form  of  a  bird,  and  if 
you  were  to  take  a  dozen  eggs  of  one  brood  of  chickens  and 
crack  one  every  few  days  while  the  mother  was  sitting  upon 
them,  each  one  would  be  more  like  a  chicken  than  the  last, 
until  the  twelfth,  if  you  opened  it  just  about  the  time  when  it 
ought  to  be  hatched,  would  be  a  perfect  chicken,  only  that  its 


CH.  XXXVIII.         VON  BAER— EMBRYOLOGY.  401 

feathers  would  not  be  yet  grown.  Now  the  study  of  the 
different  stages  of  the  development  of  the  chicken  in  the 
Q,gg.,  and  of  all  living  beings  going  througli  the  same  stages,  is 
called  E?nbryology,  and  has  become  of  immense  importance 
in  the  history  of  animals. 

You  will  remember  that  Harvey,  Malpighi,  and  many 
other  physiologists,  occupied  themselves  with  this  study  ; 
but  no  discoveries  of  very  great  importance  were  made  in 
it  before  the  time  of  Karl  von  Baer,  a  Russian  anatomist, 
who  was  born  in  1792,  Von  Baer  was  the  pupil  of  a  very 
famous  anatomist.  Professor  Dollinger,  and  while  he  was 
working  under  him  at  Wiirzburg  he  made  for  him  a 
number  of  observations  upon  the  growth  of  the  chicken 
in  the  Qgg,  which  led  him  to  study  the  embryology  of 
animals,  and  to  discover  the  remarkable  law  of  which  we 
must  now  speak. 

Before  Von  Baer's  time  it  had  always  been  supposed  that 
the  many  kinds  of  animals,  so  different  from  each  other, 
must  be  quite  unlike  from  the  very  first  moment  that  they 
began  to  grow,  but  Von  Baer  discovered  that  this  is  not  so, 
but  that  the  embrj^os  or  beginnings  of  an  ox,  a  bird,  a  lizard, 
or  a  fish,  are  so  like  each  other  that  they  can  only  be  dis- 
tinguished by  their  size  ;  and,  what  is  still  more  remarkable, 
they  remain  alike  till  they  have  been  growing  for  some  time. 
For  example,  if  you  could  watch  the  beginning  of  these  four 
animals,  there  would  be  a  certain  time  during  which  you 
could  see  no  difference  in  their  form.  Then  after  a  while 
the  fish  would  start  off  on  a  road  of  its  own,  but  still  the 
other  three  would  go  on  all  alike.  Then,  when  they  had 
grown  a  little  bigger,  the  lizard  would  branch  off,  and  only 
the  bird  and   the  ox  would   continue   to  have  the  same 


402  NINETEENTH  CENTURY,  pt.  hi. 


form,  until  lastly  the  bird  would  take  on  its  own  peculiar 
shape,  and  the  ox  would  go  on  alone,  having  passed  through 
the  same  stages  as  the  fish,  the  reptile,  and  the  bird,  before 
it  began  to  shape  itself  like  a  mammal.  You  must  notice 
carefully  that  this  does  not  mean  that  the  beginning  of  an 
ox  is  at  any  time  like  a  full-grown  fish,  which  is  a  mistake 
that  people  often  make  j  but  only  that  there  is  a  time  when 
the  embryos  of  these  animals  follow  exactly  the  same  plan. 

You  will  see,  if  you  consider  for  a  moment,  that  the  dis- 
covery of  this  curious  fact  gave  naturalists  a  new  and  much 
more  perfect  way  of  classifying  animals;  for  they  could 
actually  read  the  history  of  an  animal  by  watching  it  in  the 
earlier  stages  of  its  growth  and  seeing  at  what  point  it 
branched  off  and  put  on  special  peculiarities  of  its  own  j  and 
in  some  of  the  lower  and  more  obscure  animals  several  mis- 
takes of  classification  were  corrected  by  this  means.  There 
was  also  another  very  important  question  settled  by  Von 
Baer's  law.  It  proved  that  St.-Hilaire  was  certainly  right  in 
saying  that  animals  are  formed  on  one  plan,  having  special 
parts  altered  to  suit  their  wants,  for  here  in  the  embryo  those 
parts  can  be  seen  actually  developing  differently  in  different 
animals  out  of  the  same  beginnings.  The  study  of  em- 
bryology has  been  carried  to  great  perfection  since  Von  Baer 
published  his  '  History  of  the  Development  of  Animals  '  in 
1828;  but  though  many  names  are  better  known  than  his  in 
connection  with  it,  still  it  should  always  be  remembered  that 
he  was  the  discoverer  of  the  law  of  embryological  develop- 
ment. 


Chief  Works  consulted. — Goethe's  'CEuvres  Scientifiques,'  Faivre, 
1862;  Asa  Gray's  'Botany,'  1858;  L.  Agassiz's  '  Centenary  Address 
on  A.  von  Humboldt,'  1869  ;  HumlDoldt's  'Cosmos;'  *Biog.  Univer- 


CH.  XXXVIII,  EMBRYOLOGY.  403 

selle' — Cuvier,  GeofFroy  St. -Hilaire,  and  Lamarck  ;  Lamarck's  'Philo- 
sophic Zoologique;'  Cuvier's  '  Ossemens  Fossiles;'  GeofFroy  St. - 
Hilaire's  '  Zoologie  Generale  Suites  a  Buffon  ; '  *  Vie  et  Travaux  de 
G.  St. -Hilaire;'  Flom-ens'  'Eloge  de  Cuvier;'  'Miscellany  of  Nat. 
Hist. ' — Lauder's  *  Memoir  of  Cuvier  ; '  Jardine's  '  Naturalist's  Library 
Memoir  of  Lamarck ; '  Huxley  on  Von  Baer — Appendix  to  Baden 
Powell's  '  Unity  of  Worlds  ; '  Agassiz's  '  Systems  of  Classification.' 


404  NINETEENTH  CENTURY.  pt.  iit. 


CHAPTER   XXXIX. 

SCIENCE    OF    THE   NINETEENTH    CENTURY  (CONTINUED). 

Prejudices  which  retarded  the  Study  of  Geology — Sir  Charles  Lyell 
traces  out  the  Changes  now  going  on — Mud  carried  down  by  the 
Ganges — Eating  away  of  Sea -coasts — Eruption  of  Skaptar  Jokul — 
Earthquake  of  Calabria — Rise  and  fall  of  Land — 'Principles  of 
Geology'  published  in  1830  —  Louis  Agassiz  :  his  Early  Life  — 
De  Saussure's  Study  of  Glaciers — Agassiz  on  Europe  and  North 
America  being  once  covered  with  Ice — Boucher  de  Perthes  on 
ancient  Flint  Implements — MacEnery  on  Flint  Implements  in  Kent's 
Cavern,  with  Bones  of  Extinct  Animals — Swiss  Lake-dwellings — 
'  Antiquity  of  Man.' 

In  181 1,  when  Cuvier  published  his  work  on  *  Fossil  Re- 
mains/ William  Smith,  who,  as  you  remember  (p.  233),  first 
studied  the  rocks  of  England,  had  nearly  completed  his 
geological  map,  and  scientific  men  were  beginning,  both  in 
England  and  Germany,  to  understand  something  of  the  dif- 
ferent ages  of  the  "formations  which  have  been  laid  down 
from  time  to  time  on  the  surface  of  the  globe  ;  yet  still  they 
were  prevented  from  reading  the  past  history  of  the  world 
rightly,  by  several  false  notions  which  continued  to  prevail. 

People  had  so  long  held  the  belief  that  our  earth  had 
only  existed  a  few  thousand  years,  that  when  geologists 
began  to  find  great  numbers  of  strange  plants  and  animals 
buried  in  the  earth's  crust,  immense  thicknesses  of  rock 
laid  down  by  water,  and  whole  mountain-masses  which  must 


CH.  XXXIX.  SIjR   CHARLES  LYRLL.  405 

have  been  poured  out  by  volcanoes,  they  could  not  believe 
that  this  had  been  done  gradually  and  only  in  parts  of  the 
world  at  a  time,  as  the  Nile  and  the  Ganges  are  now  carry- 
ing down  earth  to  the  sea,  and  Vesuvius,  Etna,  and  Hecla 
are  pouring  out  lava  a  few  feet  thick  every  year.  They  still 
imagined  that  in  past  ages  there  must  have  been  mighty 
convulsions  from  time  to  time,  vast  floods  swallowing  up 
plants  and  animals  several  times  since  the  world  was  made, 
violent  earthquakes  and  outbursts  from  volcanoes  shaking 
the  whole  of  Europe,  forcing  up  mountains,  and  breaking 
open  valleys.  It  seemed  to  them  that  in  those  times  when 
the  face  of  the  earth  was  carved  out  into  mountains  and 
valleys,  table  lands  and  deserts,  and  when  the  rocks  were 
broken,  tilted  up,  and  bent,  things  must  have  been  very 
different  from  what  they  are  now.  And  so  they  made  im- 
aginary pictures  of  how  Nature  had  worked,  instead  of 
reasoning  from  what  they  could  see  happening  around 
them. 

Sir  Charles  lyell  teaches  that  the  Rocks  of  our  Earth 
have  been  formed  by  Natural  Causes,  such  as  are  still 
going  on,  1830. — The  man  who  first  broke  through  these 
prejudices  was  our  great  geologist.  Sir  Charles  Lyell,  who 
has  only  just  now  passed  away  from  among  us.  Charles 
Lyell  was  born  in  Forfarshire,  in  1797,  the  same  year  that 
Hutton  died.  From  his  earliest  childhood  he  had  a  great 
love  of  Natural  History  and  Science,  but  as  his  father 
wished  him  to  become  a  barrister,  he  went  to  Oxford  to 
follow  the  usual  course.  Here  he  attended  the  lectures  of 
Dr.  Buckland,  the  great  geologist  of  that  day,  and  this  de- 
cided him  to  devote  his  life  to  the  study  of  geology.  He 
began  first  by  examining  the  formations  round  about  his 
own  home  in  Forfarshire,  and  he  soon  became  convinced, 


406  NINETEENTH  CENTURY.  pt.  ill. 

as  Hutton  had  been  before  him  (see  p.  219),  that  we  can 
only  learn  the  past  history  of  the  earth  by  observing  the 
causes  now  at  work. 

What  Hutton  had  suggested  Lyell  worked  out.  He  col- 
lected with  great  care  all  that  is  known  of  changes  going  on 
now  all  over  the  world,  and  the  causes  which  produce  them. 
Among  these  were — 

istly.  The  fall  of  rain,  and  how  it  wears  away  the  earth 
and  carries  it  off  in  little  rills  to  the  river. 

2ndly.  The  amount  of  mud  carried  by  mighty  streams, 
such  as  the  Ganges,  the  Nile,  and  the  Mississippi,  and  laid 
down  in  the  sea  at  their  mouths. 

3rdly.  The  amount  of  lime,  iron,  and  other  minerals 
brought  up  by  springs  from  the  inside  of  the  earth,  and 
thrown  down  on  the  surface. 

4thly.  The  tides  and  currents  of  the  sea,  and  how  they 
wash  up  fresh  land  on  some  coasts  and  eat  away  th^  land 
on  others. 

5thly.  The  growth  of  corals  in  the  sea,  and  how  remains 
of  their  skeletons  become  cemented  into  limestone. 

6thly.  The  volcanoes  which  are  throwing  out  lava,  and 
how  much  they  have  thrown  out  in  historical  times. 

7thly.  The  different  earthquakes  which  man  has  wit- 
nessed, how  they  have  broken  and  dislocated  the  land, 
raising  it  in  some  places,  as  in  New  Zealand,  and  causing 
it  to  sink  in  others,  as  at  New  Madrid,  in  America. 

8thly.  The  way  in  which  plants  and  animals  are  buried 
in  the  mud  of  lakes,  or  at  the  mouths  of  rivers,  or  in  peat  and 
sand. 

All  these,  and  many  other  changes  which  are  taking 
place  all  over  the  world  in  the  present  day,  Lyell  studied 
with  great  accuracy,  and  then  began  a  book  to  show  that 


cii.  XXXIX.  SIR   CHARLES   LYELL.  407 


what  we  find  in  the  rocks  might  all  have  been  produced  by 
such  causes  as  these,  without  imagining  any  extraordinary 
violence  of  nature. 

While  writing  this  book  he  went  with  another  celebrated 
geologist,  Murchison,  to  Italy  and  Sicily,  and  there  he 
studied  not  only  the  rocks  which  the  volcanoes  of  Vesuvius 
and  Etna  have  been  building  up  for  ages,  but  he  also  saw 
at  Syracuse  and  other  places  enormous  beds  of  limestone 
filled  with  shells  of  kinds  which  may  still  be  found  living. 
The  immense  thickness  of  these  limestone  beds,  amounting 
in  some  places  to  700  and  800  feet,  astonished  him  greatly. 
He  knew  they  must  all  have  been  formed  slowly  beneath 
the  sea,  out  of  the  remains  of  corals  and  other  animals, 
whose  skeletons  or  shells  are  composed  of  lime,  and  that 
they  must  afterwards  have  been  raised  up  to  the  height  of 
3,000  feet  above  the  sea,  at  which  he  found  them;  and 
when  he  thought  of  the  time  which  this  must  have  taken, 
and  Remembered  that  it  had  all  happened  since  the  other 
great  masses  of  rocks  below,  containing  extinct  shells,  had 
been  formed,  he  felt  more  than  ever  convinced  that  the  world 
must  be  very  old,  to  have  allowed  time  for  all  the  wonderful 
changes  that  have  taken  place. 

In  1830  his  book  was  published,  and  though  it  met  with 
great  opposition  because  men's  minds  were  prejudiced  the 
other  way,  yet  his  facts  could  not  be  denied.  He  showed, 
for  example,  on  the  one  hand  that  the  river  Ganges  in  India 
carries  down  every  year,  and  deposits  in  the  sea,  as  much 
mud  as  would  make  sixty  of  the  great  pyramids  of  Egypt, 
and  which  if  it  was  brought  in  ships  would  require  2,000 
full- sized  merchant  vessels  laden  with  mud  to  sail  down  the 
Ganges  every  day.  Here,  then,  was  an  example  of  rocks 
being  now  laid  down  in  the  sea,  not  by  violent  floods  and 


408  NINETEENTH  CENTURY.  pt.  hi. 


sudden  catastrophes,  but  so  quietly  that  no  one  even  notices 
that  nature  is  at  work. 

Then,  on  the  other  hand,  he  pointed  out  how  in  our  own 
little  island,  on  the  coasts  of  Yorkshire. and  Norfolk,  the  sea 
eats  away  the  cliffs,  so  that  towns  such  as  Auburn,  Hartbum, 
and  Hyde  in  Yorkshire,  which  are  marked  upon  old  maps, 
have  been  entirely  washed  away,  and  the  ground  on  which 
they  stood  has  been  spread  out  on  the  bottom  of  the  ocean  ; 
and  yet  this  is  done  so  gradually,  year  by  year,  that  new 
towns  of  the  same  name  are  built  up  farther  inland,  and  no 
one  disturbs  themselves  about  the  loss. 

Then  to.  account  for  the  huge  masses  of  basalt  and  lava 
which  are  found  in  the  earth's  crust,  he  reminded  his  readers 
of  the  great  eruption  of  the  volcano  called  Skaptar  Jokul  in 
Iceland,  which  took  place  in  1783.  In  this  eruption  the 
torrent  of  lava  was  ninety  miles  in  length,  from  seven  to 
fifteen  miles  in  breadth,  and  in  some  places  600  feet  deep, 
and  the  whole  mass  poured  out  would  have  made  a  mountain 
as  big  as  Mont  Blanc. 

He  then  went  on  to  give  accounts  of  the  remarkable 
earthquakes  which  have  taken  place  in  times  of  history  : 
the  earthquakes  in  India,  in  Java,  and  especially  in  Cala- 
bria, in  1783,  when  new  lakes  were  formed  by  the  sinking 
in  of  the  ground,  and  the  rivers  were  made  to  run  in  new 
channels.  He  showed  also  how  the  height  of  land  is  some- 
times changed  in  volcanic  countries  j  as  on  the  coast  of 
Italy,  near  Naples,  where  the  ground  on  which  the  famous 
Temple  of  Serapis  stands  can  be  proved  to  have  been 
raised  and  depressed  twice  even  in  historical  times. 

And  besides  all  these  obvious  changes  which  men  cannot 
help  noticing,  he  proved  that  other  quiet  and  unnoticed  risings 
and  fallings  of  land  are  taking  place ;  as,  for  example,  in  Nor- 
way and  Sweden,  where  the  land  is  rising  out  of  the  sea  in 


cir.  XXXIX.  SIR   CHARLES  LYELL.  409 

some  places  at  the  rate  of  about  two  or  three  feet  in  a  cen- 
tury ;  and  in  Greenland,  where  it  is  sinking,  so  that  huts 
built  near  the  shore  have  to  be  moved  inland  because  they 
are  becoming  submerged  in  the  sea. 

These  are  a  very  few  of  the  facts  which  you  can  under- 
stand, by  which  Lyell  demonstrated  that  the  surface  of  our 
earth  is  always  undergoing  changes  in  our  own  day,  and  that 
by  similar  changes  going  on  in  past  times  the  whole  of  the 
crust  of  our  earth  may  have  been  built  up  and  carved  out. 
In  addition  to  this  he  showed  how  plants  and  animals  are  now 
being  buried  in  mud  and  earth,  and  how  their  remains  are 
washed  into  caves,  or  preserved  in  peat-mosses  ;  thus  afford- 
ing us  examples  of  the  way  in  which  the  remains  of  ancient 
animals  have  become  entombed  in  the  earth's  crust. 

Thus  Sir  Charles  Lyell  taught  men  to  read  the  true  his- 
tory of  the  earth.     It  is  difficult  in  the  present  day  to  under- 
stand rightly  how  great  a  work  he  accomplished,  for  though 
his  ideas  were  ridiculed  in  the  beginning,  yet  he  lived  long 
enough  to  see  all  men  agree  with  him,  and  his  doctrines 
received  as  self-evident  truths.     Like  all  other  great  men, 
he  was  humble  and  reverent  in  his  study  of  nature.     His 
one  great  desire  was  to  arrive  at  truth,  and  by  his  con- 
scientious and  dispassionate  writings  he  did  much  to  per- 
suade people  to  study  geology  calmly  and  wisely,  instead 
of  mixing  it  up  with  angry  disputes,  like  those  which,  in 
the  time  of  Galileo,  disfigured  astronomy.      He  travelled 
a  great  deal,  especially  in  America,  and  worked  out  a  great 
many  facts  in  geology.     But  in  future  ages  his  name  will 
stand  out  among  those  of  other  geologists  chiefly  as  having 
shown  that  the  changes  in  the  crust  of  our  eai'th  have  been 
brought  about  in  the  cou7'se  of  long  ages  by  causes  like  those 
which  are  still  in  action. 

After  the  year  1830,  when  his  '  Principles  of  Geology  ' 
19 


4IO  NINETEENTH  CENTURY.  pt.  hi. 

was  first  published,  the  study  of  this  science  went  on  very 
rapidly  indeed.  As  with  all  the  other  sciences  of  the  nine-, 
teenth  century,  you  must  read  the  details  in  special  works  ; 
but  there  are  two  great  discoveries  which  we  must  mention 
very  shortly  here.  These  are — ist.  The  fact  that  much  of 
temperate  Europe,  Asia,  and  America  was  at  one  time 
covered  with  ice,  as  Greenland  is  now ;  and  2nd,  that 
man  has  lived  upon  the  earth  much  longer  than  was  once 
supposed. 

Louis  Agassiz,  1807-1874. — The  man  whose  name  will 
always  be  remembered  as  having  first  traced  out  the  wonder- 
ful history  of  the  great  ice-period  is  Agassiz,  the  famous 
Swiss  naturalist,  who  was  bom  in  1807  at  Mottier,  near 
Neuchatel,  and  died  in  1874  in  America. 

Louis  Agassiz  was  the  son  of  a  Swiss  pastor,  and  he 
forms  one  among  many  bright  examples  in  the  history  of 
science,  of  men  who  cared  neither  for  wealth,  advance- 
ment, nor  ease,  but  for  the  study  of  nature  alone,  and  the 
grand  truths  to  be  obtained  by  it.  After  receiving  a  good 
education  in  the  Swiss  and  German  Universities,  living 
frugally  and  economically,  -as  students  can  on  the  Continent, 
he  took  his  degree  of  Doctor  of  Medicine  at  Munich  in 
1829,  having  already  written  several  important  papers  on 
zoology.  In  1832  he  was  made  Professor  of  Natural  His- 
tory at  the  University  of  Neuchatel  \  and  in  1833  he  pub- 
lished his  work  on  '■  Fossil  Fishes,'  the  expenses  of  the  book 
being  liberally  paid  by  Humboldt.  In  1839  he  published 
his  grand  work  on  the  *  Fresh-water  Fishes  of  Europe,* 
which  cost  him  so  much  that  he  was  very  poor  for  years 
afterwards. 

There  are  very  touching  passages  in  some  of  Agassiz's 
private  letters    at   this   early  period,  when  he  had  a  hard 


CH.  XXXIX.  AGASSIZ.  411 

struggle  with  life.  His  enthusiasm  breathes  out  so  natu- 
rally, and  he  speaks  so  regretfully  of  want  of  money,  not 
for  himself,  but  the  work  he  longed  to  complete  ;  while 
his  gratitude  is  so  sensible  and  heartfelt  towards  those  who 
helped  him  to  bring  out  these  splendid  additions  to  the 
science  of  zoology.  His  was  a  warm-hearted,  earnest,  and 
active  nature,  and  he  was  beloved  by  all  who  knew  him. 
It  is  pleasant  to  think  that  the  Americans,  among  whom 
he  spent  the  latter  half  of  his  life,  from  1846  to  1874,  ap- 
preciated him  fully  ;  so  much  so  that  Mr.  Anderson,  a 
rich  tobacco  merchant  of  New  York,  presented  him  in 
1873  with  the  island  of  Penikese,  one  of  the  Elizabeth 
islands,  north  of  New  York,  and  with  funds  to  establish 
there  a  marine  naturalist's  school.  The  last  year  of  Agassiz's 
life  was  spent  chiefly  on  this  island,  training  up  a  group  of 
young  naturalists. 

Agassiz  proves  that  parts  of  northern  Europe  and 
North  America  must  once  have  been  covered  with  Great 
Fields  of  Ice,  1840. — It  is,  however,  of  the  early  part  of 
Agassiz's  life,  while  he  was  still  in  Switzerland,  that  we  must 
now  speak.  Although  his  chief  study  was  zoology,  yet  he 
could  not  live  at  Neuchatel,  and  travel  about  the  Alps  without 
being  struck  with  those  mighty  rivers  of  ice,  called  glaciers, 
which  creep  slowly  down  the  valley  of  the  Alps  in  Switzerland, 
carrying  with  them  stones  and  rubbish.    (See  Fig.  62,  p.  412.) 

These  glaciers  are  formed  by  the  snow,  which  collects 
on  the  tops  of  high  mountains,  and  sliding  down,  becomes 
pressed  more  and  more  firmly  together  as  it  descends  into 
the  valleys,  until  it  is  moulded  into  solid  ice,  creeping 
slowly  onwards  between  the  mountains,  and  carrying  with  it 
sand,  stones,  and  often  huge  pieces  of  rock  which  fall  upon 
it.     At  last  one  end  of  this  ice-river  reaches  a  point  where 


412 


NINETEENTH  CENTURY. 


PT.  III. 


f 


the  air  is  warm  enough  to  melt  it,  and  here  it  flows  gradually 
away  as  water,  leaving  the  stones  and  rubbish  it  has  brought 
down  lying  in  a  confused  heap,  which  is  called  a  moraine. 

Towards  the  end  of  the  eighteenth  century  a  famous 
geologist,  named  De  Saussure,  spent  much  time  in  examining 

Fig.  62. 


Glacier  carrying  down  Stones  and  Rubbish  (Lyell). 

the  glaciers  of  the  Alps,  and  pointed  out  how  they  are  now 
forming  large  deposits  in  the  valleys,  out  of  these  heaps  of 
rubbish  which  they  bring  down  from  the  mountains.  Since 
his  time  many  geologists  had  taken  up  the  study,  but  it  was 
Professor  Agassiz  who  first  spelled  out  the  wonderful  history 
we  can  learn  from  it,  about  the  former  climate  of  our  hemi- 
sphere.    He  noticed  that  rocks  over  which  a  glacier  has 


CPi.  XXXIX.  GLACIERS.  413 

moved,  are  polished  and  grooved  by  the  rough  stones  and 
sand  frozen  into  the  bottom  of  the  ice,  just  in  the  same  way 
as  a  piece  of  wood  is  scraped  by  the  sharp  iron  at  the 
bottom  of  a  plane  ;  and  by  these  glacial  scratches,  or  stri(B, 
as  they  are  called,  he  could  tell  where  glaciers  had  been, 
even  though  there  was  nothing  else  to  show  that  ice  had 
ever  existed  in  the  country. 

Now,  when  he  began  to  examine  the  slopes  of  the  Alps 
many  hundred  feet  above  the  present  glaciers,  and  also  in 
places  where  it  is  now  too  hot  for  ice  to  remain,  he  found 
to  his  surprise  numbers  of  these  glacial  striae  and  also 
remains  of  huge  moraines,  showing  that  the  glaciers  of 
olden  time  must  once  have  been  much  larger  and  have 
stretched  farther  down  the  valley  than  they  do  now.  And 
what  was  still  more  strange,  these  same  marks  were  to  be 
seen  on  the  Jura  Mountains,  on  the  other  side  of  Switzerland, 
where  there  are  never  any  glaciers  at  present ;  moreover,  on 
the  Jura  there  were  found  huge  blocks,  some  of  them  as 
big  as  cottages,  which  were  not  made  of  the  same  materials 
as  the  hills  on  which  they  rested,  but  were  broken  pieces  of 
rock  such  as  are  now  only  found  on  the  Alps. 

It  was  clear,  then,  that  these  enormous  pieces  of  stone 
must  have  been  carried  right  across  Switzerland  from  the  Alps 
near  Mont  Blanc,  and  across  the  lake  of  Geneva,  which  is 
1,000  feet  deep,  and  then  deposited  on  the  Jura  range  near 
Neuchatel,  where  one  block  of  Alpine  gneiss,  called  the 
Pierre-a-Bot,  as  large  as  a  good-sized  cottage,  sits  perched 
on  a  mountain  600  feet  above  the  top  of  the  lake.  How 
had  these  blocks  travelled  across  the  Swiss  plains  ?  No  flood 
could  have  carried  them,  for  they  were  too  heavy,  and  be- 
sides they  were  not  smooth  as  stones  are  which  have  been 
rolled  in  water,  but  were  rough  with  sharp  edges.     Agassiz 


414  NINETEENTH  CENTURY.  pt.  in. 

was  convinced,  therefore,  that  they  must  have  been  carried 
by  ice,  and  that  huge  glaciers  must  once  have  come  down 
from  the  high  Alps  right  across  Switzerland,  filling  the  lake 
of  Geneva  with  ice,  and  carrying  these  blocks  with  them,  as 
modern  glaciers  do  now  in  the  Swiss  valleys. 

This  was  a  marvellous  history,  for  it  showed  that  all  the 
lower  land  of  Switzerland  must  once  have  beeu  buried  in 
ice,  but  other  facts  afterwards  came  to  light  which  were  more 
wonderful  still.  In  1840  Professor  Agassiz  came  over  to 
visit  Great  Britain,  and  when  he  went  to  Scotland  with  Dr. 
Buckland  his  practised  eye  discovered  at  once  in  the  High- 
lands glacial  scratchings,  remains  of  moraines,  and  blocks 
which  had  been  carried  by  ice;  and  soon  it  became  evi- 
dent that  these  were  not  confined  to  Scotland,  for  Dr. 
Buckland  recognised  them  again  in  Wales  and  the  North  of 
England,  where  moraines  and  erratic  blocks  are  to  be  seen 
in  all  parts  of  the  country.  So  that  here,  too,  in  our  little 
island,  there  must  have  been  at  one  time  huge  glaciers  as 
large  as  those  now  found  in  the  Alps. 

Nor  was  this  all ;  for  when  once  geologists  knew  where 
to  look  for  these  signs  of  glaciers,  it  began  to  be  discovered 
little  by  little  that  parts  of  all  the  northern  countries  of 
Europe,  Norway,  Sweden,  Russia,  Germany,  Switzerland, 
Northern  Italy,  England,  and  even  on  the  other  side  of  the 
Atlantic,  Canada  and  North  America,  have  been  smoothed 
and  scratched  ;  and  huge  erratic  (or  wandering)  blocks  have 
been  scattered  over  them,  showing  that  in  very  remote  ages 
(yet  still  while  very  nearly  the  same  kinds  of  plants  and 
animals  as  now  were  living  upon  the  globe),  the  temperate 
parts  of  our  northern  hemisphere  must  have  been  intensely 
cold,  causing  a  large  part  of  these  countries  to  be  covered 
with  great  fields  of  ice,  as  Greenland  is  in  the  present  day. 


CH.  XXXIX.  BOUCHER  DE  PERTHES.  415 

And  just  as  we  see  now  that  icebergs  break  off  from  the 
Greenland  glaciers,  carrying  with  them  stones  and  mud,  and 
dropping  them  at  the  bottom  of  the  sea ;  so  in  those  times 
icebergs  floated  over  many  of  the  valleys  of  Europe,  which 
were  then  submerged  beneath  the  ocean.  You  may  see  in 
the  railway- cuttings  of  Wales  and  in  the  sea-cliffs  in  the 
coast  of  Yorkshire  and  Norfolk  huge  masses  of  glacial  drift, 
as  it  is  called,  made  of  mud  and  stones  confusedly  mixed 
together,  which  were  dropped  from  icebergs  travelling  south- 
wards from  the  ice-fields. 

This  period  of  cold  is  called  by  geologists  the  '  Glacial 
Period  ; '  and  when  you  read  works  on  geology  you  will  see 
that  it  explains  in  a  wonderful  manner  many  curious  facts 
in  the  later  history  of  our  earth,  and  the  distribution  of 
plants  and  animals  upon  it.  For  the  present  it  is  enough 
for  you  to  remember  that  Agassiz  first  pointed  out  the  signs 
of  this  cold  period,  and  that  this  discovery  was  one  of  the 
earliest  rewards  of  a  patient  study  of  causes  which  are  going 
on  now ;  for  it  is  from  the  ice-action  in  Switzerland  and 
Greenland  in  the  present  day,  that  we  are  able  to  understand 
how  these  huge  ice-fields  carried  down  erratic  blocks  and 
the  mud  of  moraines  during  the  Glacial  Period. 

Geological  Proofs  that  Man  lived  upon  the  Earth  in  Ages 
long  gone  by,  with  Animals  which  are  now  extinct,  1847. 
— The  second  remarkable  discovery  which  has  been  made 
in  geology  in  this  century  is  that  of  the  antiquity  of  man;  or 
the  fact  that  man  must  have  existed  upon  our  earth  long 
before  the  very  earliest  times  of  history  or  tradition  ;  in  an 
age  when  an  elephant  and  a  hyaena,  of  extinct  species, 
roamed  about  England  and  France,  together  with  some 
other  strange  animals  which  are  not  now  to  be  found  upon 
the  globe. 


1 


41 6  NINETEENTH  CENTURY.  pt.  hi. 

This  discovery,  which  was  not  believed  for  a  long  time, 
was  first  announced  by  a  French  geologist,  M.  Boucher  de 
Perthes,  in  the  year  1847.  It  happened  that  near  this 
gentleman's  house,  at  Abbeville  in  Picardy,  gravel-pits  had 
been  dug  from  time  to  time  for  repairing  the  fortifications  of 
the  town,  or  mending  the  roads.  During  these  excavations, 
in  the  beginning  of  the  century,  a  great  many  bones  of  ani- 
mals had  been  dug  up  and  sent  to  Cuvier  at  Paris ;  and  he 
stated  that  some  of  them  belonged  to  animals  slightly  dif- 
ferent from  any  now  living,  though  not  so  ancient  as  those 
which  came  from  under  Paris  (see  p.  397).  This  showed 
that  these  beds  of  sandstone  must  have  been  formed  long 
before  the  times  of  history  or  the  earliest  ages  in  which 
man  was  supposed  to  have  been  upon  the  earth.  People, 
therefore,  were  much  astonished  when  M.  Boucher  de  Perthes 
stated  in  1847  that  he  had  found  very  rough  stone  weapons 
in  these  beds,  such  as  savages  might  use,  seeming  to  prove 
that  men  must  have  been  living  at  the  same  time  as  these 
extinct  animals. 

This  seemed  so  incredible  that  scientific  men  would  not 
even  listen  to  Boucher  de  Perthes'  arguments  in  his  work 
called  *  Antiquites  Celtiques,'  and  it  was  not  till  1858,  when 
one  of  our  best  living  geologists,  Mr.  Prestwich,  went  to 
Abbeville  and  took  a  well-shaped  flint  hatchet  out  of  the 
undisturbed  gravel  with  his  own  hands,  that  people  began  to 
believe  that  human  beings  must  have  been  living  in  the 
world  much  longer  than  had  hitherto  been  believed.  When, 
however,  this  was  once  acknowledged  to  be  true,  several 
new  facts  sprang  up  to  confirm  the  theory.  Many  years 
before,  in  1825,  a  Roman  Catholic  priest,  the  Rev.  J.  Mac 
Enery,  had  found  flint  tools,  with  the  bones  of  the  extinct 
elephant,  hysena,  and  bear,  in  a  cave  called  Kent's  Hole, 


CH.  XXXIX.  LAKE-DWELLINGS,  417 

near  Torquay,  but  very  little  notice  had  been  taken  of  this 
discovery.  Now,  however,  they  were  thoroughly  studied, 
and  they  showed  clearly  that  men  who  made  rough  flint 
tools  (such  as  are  still  made  by  savages  in  many  parts  of  the 
world)  must  have  lived  in  England,  together  with  a  bear, 
an  elephant,  a  lion,  and  a  hyaena,  all  of  species  v/hich  have 
now  ceased  to  exist. 

Discovery  of  the  Swiss  Lake- dwellings,  1853.— Again, 
in  Switzerland,  most  curious  discoveries  have  been  made, 
giving  us  proofs  of  three  distinct  periods  in  the  life  of  man- 
kind. In  the  year  1853,  when  the  Swiss  lakes  were  very 
low  in  consequence  of  a  long  drought,  WQoden  piles  were 
observed  to  rise  above  the  water ;  and  when  these  were 
examined  by  the  Swiss  antiquarians  it  was  found  that  they 
were  foundations  of  wooden  villages,  which  had  been  built 
by  the  inhabitants  of  Switzerland  in  past  ages.  They  stood 
some  way  out  in  the  lake,  and  must  have  been  joined  to 
the  shore  by  wooden  bridges  which  the  villagers  could  lift 
up  when  enemies  came  to  attack  them,  and  thus  become 
protected  by  the  water  surrounding  them.  Habitations  of 
this  kind  are  built  in  the  present  day  by  the  natives  of  Papua 
or  New  Guinea. 

Down  below  the  piles  in  the  mud  of  the  Swiss  lakes  a 
great  number  of  tools,  cooking  utensils,  bones  of  animals,  and 
even  burnt  bread  and  corn,  were- found;  and  the  remarkable 
thing  was,  that  the" different  kinds  of  tools  showed  that  the 
villages  did  not  all  belong  to  one  age.  In  a  few,  on  the 
lakes  of  Bienne  and  Neuchatel,  iron  tools  were  buried,  show- 
ing that  when  these  villages  were  inhabited  men  knew  how 
to  melt  iron  out  of  the  rocks  and  make  it  into  tools.  These 
villages  must  have  been  about  the  time  of  the  Romans. 

In  others,  however,  .only  bronze  tools  were  found,  and 


41 8  NINETEENTH  CENTURY.  pt.  hi. 

these  were  much  older,  because  bronze  was  used  long  before 
iron  was  discovered.  And  lastly  in  some,  tools  of  stone 
only  have  been  found,  some  beautifully  polished,  but  others 
rough  and  rude,  showing  that  the  men  avIio  used  them  must 
have  been  mere  savages  like  the  Australians  now  ;  and  yet 
the  oldest  of  these  lake-villages  have  no  bones  of  extinct 
animals  in  them,  and  therefore  cannot  be  so  ancient  as  those 
men  whose  tools  were  found  in  the  cavern  at  Torquay  and 
the  sandpits  of  Abbeville,  or  as  have  since  been  found  in 
England,  Denmark,  Germany,  America,  and  indeed  in 
almost  all  countries. 

It  is  impossible,  without  a  knowledge  of  geology,  to  realise 
how  very  long  ago  these  last-mentioned  men  must  have  lived. 
But  when  I  tell  you  that  since  their  tools  were  buried  in  the 
rocks,  there  has  been  time  for  beds  of  immense  thickness  to 
be  laid  down  little  by  little,  as  the  Ganges  is  laying  them 
down  now  ;  for  parts  of  the  French  valleys  to  be  gradually 
washed  away,  and  their  shape  altered ;  for  rivers  to  change 
their  courses,  and  vast  beds  of  peat  to  grow  over  the 
bottoms  of  the  valleys  ;  and,  more  than  all,  for  whole  races 
of  animals  which  once  lived  to  have  died  quite  away  from 
the  face  of  the  earth,  you  may  perhaps  form  some  idea  of  the 
long  ages  that  man  must  have  been  upon  our  globe.  This 
history,  however,  is  so  new  and  as  yet  so  little  understood, 
that  it  cannot  be  explained  in  a  few  pages.  You  will  find 
all  the  proofs  of  it  given  in  Sir  Charles  Lyell's  work  on  the 
*  Antiquity  of  Man,'  in  which  they  were  first  collected  in  1863  ; 
and  you  must  remember  the  fact,  that  man  is  very  ancient, 
as  one  of  the  great  discoveries  of  the  nineteenth  century. 


CMef  Worh  consulted. — Lyell's  '  Principles  of  Geology,'  'Elements 
of  Geology,'  '  Antiquity  of  Man  ; '  Lubbock's  '  Prehistoric  Times  ; ' 
'Quarterly  Geological  Journal,'  vol.  xxx.  :  Obituary  of  Agassiz. 


CH.  XL.  BIOLOGY. 


419 


CHAPTER  XL. 

SCIENCE   OF   THE    NINETEENTH    CENTURY   (CONTINUED). 

Facts  which  led  Naturalists  to  believe  that  the  Different  Kinds  of 
Animals  are  descended  from  Common  Ancestors  —  All  Animals 
of  each  Class  formed  on  one  Plan — Embryological  Structure — 
Living  and  Fossil  Animals  of  a  Country  resemble  each  other  — 
Gradual  Succession  of  Animals  on  the  Globe — Links  between  Dif- 
ferent Species— Darwin's  Theory  of  Natural  Selection — Wallace 
worked  out  the  same  Theory  independently — Sketch  of  the  Theory 
of  Natural  Selection — Selection  of  Animals  by  Man — Selection  by 
Natural  Causes — Difficulties  in  Natural  History  which  are  explained 
by  this  Theory — Foolish  Prejudices  against  it — Concluding  Remarks 
on  the  History  of  Science. 

Facts  wMch  have  led  Naturalists  to  believe  that  the 
different  kinds  of  Animals  are  descended  from  common 
Ancestors. — We  now  come  to  the  first  attempt  of  any  value 
which  has  ever  been  made,  to  explain  how  the  different  kinds 
of  animals  and  plants  have  been  produced.  This  question 
is  so  very  difficult,  and  seems  so  much  beyond  our  grasp, 
that  we  find  very  few  people  throughout  the  history  of 
science  who  even  tried  to  answer  it.  Aristotle,  it  is  true, 
remarked  that  we  can  trace  such  a  close  resemblance 
between  the  different  species,  from  the  lowest  plant  up  to 
the  highest  animal,  as  would  seem  to  show  they  are  related 
to  each  other  (p.  16).  Bonnet,  too,  thought  that  animals 
were  developed  from  lower  into  higher  forms  (p.  202) ;  and 
Lamarck,  as  we  have  seen,  boldly  suggested  the  same  expla- 
nation (p.  391). 


430  NINETEENTH  CENTURY.  ft.  hi. 

But  people  in  general  treated  these  as  mere  wild  specu- 
lations, and  were  content  to  say  that  God  had  created 
animals,  just  in  the  same  way  as  they  said  that  the  stars 
were  created  by  Him,  without  pausing  to  consider  how  He 
has  created  them. 

Since  the  time  of  Buff  on  and  Linnseus,  however,  many 
new  facts  had  gradually  been  brought  to  light  about  living 
animals ;  and  fossil  species  had  been  dug  out  of  the  earth, 
showing  that  many  different  forms  had  lived  upon  our  globe, 
one  after  the  other  j  and  these  new  discoveries  led  naturalists 
to  speculate  whether  some  clue  might  not  be  found  to 
explain  this  long  succession  of  living  beings. 

Then  again,  as  naturalists  spread  all  over  the  world  and 
many  new  forms  of  animals  and  plants  became  known,  it  was 
found  to  be  more  and  more  difficult  to  separate  the  different 
species  and  to  say  which  are  and  which  are  not  descendants 
of  one  parent.  Linnaeus,  as  we  have  seen  (p.  392),  pointed 
this  out  in  the  case  of  plants,  and  wild  roses  are  a  very  good 
example  of  it ;  for  the  different  kinds  run  so  much  into  each 
other  that  while  one  of  our  best  botanists  has  divided  them 
into  seventeen  s^ecies^  another  thinks  that  many  of  these  must 
have  come  from  the  same  parent,  and  that  only  five  species 
can  be  distinguished.  Again,  among  insects,  the  well-known 
naturalist,  Mr.  Bates,  has  shown  that  on  the  Amazons  in  South 
America  it  is  often  impossible  to  tell,  among  some  families 
of  butterflies,  which  are  the  same  species  and  which  keep 
apart  from  each  other.  Facts  like  these,  of  the  relationship 
of  living  beings,  had  long  been  forcing  themselves  upon 
naturalists,  and  this  was  one  of  the  reasons  given  by  Lamarck 
for  supposing  animals  to  be  all  descended  from  a  few  simple 
forms. 

All  the  Animals  of  each  Class  formed  on  the  same 


CH.  XL.  DESCENT  OF  ANIMALS.  421 

Plan. — Another  reason  was  that  curious  agreement  in  the 
bones  of  different  animals  which  had  become  more  and 
more  noticed  ever  since  the  time  of  John  Hunter,  and  which 
Geoffroy  St.-Hilaire  insisted  upon  so  strongly.  Why  should 
the  animals  of  one  class  (such  as  the  vertebrate  or  back- 
boned class)  be  formed  all  on  one  plan  even  to  the  most 
minute  bones  ;  so  that  the  wing  of  a  bat,  the  front  leg  of  a 
horse,  the  hand  of  a  man,  and  the  flapper  of  a  porpoise,  are 
all  made  of  the  same  bones,  which  have  either  grown  together, 
or  lengthened  and  spread  apart,  according  to  the  purpose 
they  serve  ?  And,  more  curious  still,  why  should  some 
animals  have  parts  which  are  of  no  use  to  them,  but  only 
seem  to  be  there  because  other  animals  of  the  same  class 
also  have  them.  Thus  the  whale  has  teeth  like  the  other 
mammalia,  but  they  never  pierce  through  the  gum  ;  and  the 
boa- constrictor  has  the  beginnings  of  hind  legs  hidden  under 
its  skin,  though  they  never  grow  out.  Here  again  it  seemed 
extraordinary,  if  a  boa-constrictor  and  a  whale  were  created 
separately,  that  they  should  be  made  with  organs  which 
are  quite  useless;  while,  on  the  other  hand,  if  they  were 
descended  from  the  same  ancestor  as  other  reptiles  and 
mammalia  who  have  teeth  and  hind  legs,  they  might  be 
supposed  to  have  inherited  these  organs ;  just  as,  for  ex- 
ample, a  child  sometimes  has  a  mole  or  other  mark  upon  its 
body  in  exactly  the  same  place  as  its  great  grandfather  had 
before  it. 

Embryos  of  Animals  alike  in  Structure. — Another  still 
more  remarkable  fact  was  that  pointed  out  by  Von  Baer, 
that  the  higher  animals,  such  as  quadrupeds,  before  they  are 
perfectly  formed,  cannot  be  distinguished  from  the  embryos 
of  other  and  lower  animals,  such  as  fish  and  reptiles.  If 
animals  were   created  separately  why   should  a   dog  begin 


1 


422  NINETEENTH  CENTURY.  pt.  hi. 

like  a  fish,  a  lizard,  and  a  bird,  and  have  at  first  parts  which 
it  loses  as  it  grows  into  its  own  peculiar  form  ? 

Living  Animals  of  a  Country  agree  with,  the  Fossil 
ones. — These  were  facts  entirely  belonging  to  living  creatures, 
but  now  others  sprang  up  about  fossil  species  which  were 
equally  puzzling.  We  know  that  certain  animals  are  only 
found  in  particular  countries  ;  kangaroos  and  pouched  ani- 
mals, for  example,  in  Australia  ;  and  sloths  and  armadillos 
in  South  America.  Now  it  is  remarkable  that  all  the  fossil 
quadrupeds  in  Australia  are  also  pouched  animals,  though 
they  are  of  different  kinds  and  larger  in  size  than  those  now 
living ;  and  in  the  same  way  different  species  of  sloths  and 
armadillos  are  found  fossil  in  South  America  ;  while  in  the 
rocks  of  Europe  fossil  mammalia  are  found,  only  slightly 
different  in  form  from  those  which  are  living  there  now. 
Naturalists  therefore  asked  themselves  again — '  Would  it  not 
seem  likely  that  the  living  pouched  animals  of  Australia 
and  the  sloths  and  armadillos  of  America  are  the  descen- 
dants of  the  dead  ones  in  the  rocks,  although  they  have  in 
the  course  of  long  ages  become  rather  different  from  them  j 
while  oxen,  bears,  wolves,  &c.,  are  also  the  descendants  of 
those  which  are  found  buried  in  the  rocks  of  Europe  ? 

Gradual  succession  of  Animals  which  have  appeared 
upon  the  Globe. — This  seemed  still  more  likely  as  the  study 
of  geology  advanced,  and  it  became  clear  that  a  gradual  suc- 
cession of  higher  and  higher  animals  had  appeared  upon  the 
globe.  Thus,  in  the  oldest  rocks  containing  fossils,  we  find  no 
monkeys,  no  quadrupeds,  no  reptiles,  no  amphibians  such 
as  our  frogs,  but  only  shells  of  marine  animals,  and  a  few 
bones  of  fishes,  of  kinds  quite  different  from  those  now  living. 

Then  in  rocks  above  these  we  find  the  fish  becoming 
very  abundant  and  varied,  and  higher  still  we   meet  with 


CH.  XL.  SUCCESSION  OF  ANIMALS.  423 

footprints  of  some  animal  with  feet ;  and  the  bones  of  an 
amphibian,  somewhat  Hke  a  frog,  are  next  found.  In  these 
times  the  fish  began  to  cease  to  be  monarchs  of  the  water,  for 
a  Httle  higher  up  huge  swimming  reptiles,  like  our  crocodiles 
and  lizards,  but  much  larger,  have  left  their  bones  in  the 
rocks.  Next  come  reptiles  with  wings,  which  measure  six- 
teen feet  across  from  tip  to  tip,  and  we  must  picture  these 
huge  flying  lizards,  with  wings  like  bats,  roaming  over  the 
globe  with  no  higher  animals  to  persecute  them. 

But  they  were  only  to  have  their  turn,  for  in  rocks  formed 
a  little  later  there  appear  two  skeletons,  one  of  a  small  crea- 
ture half  reptile  half  bird,  about  the  size  of  a  pigeon,  and  the 
other  of  a  real  bird  with  some  of  its  feathers  still  remaining ; 
and  in  beds  of  about  the  same  age  there  occurs  the  jaw  of 
a  small  insect-eating  animal  something  like  an  ant-eater. 
Birds  and  quadrupeds  therefore  had  now  begun  to  exist,  and 
soon  the  bones  of  pouched  animals  are  found,  and  then  of 
mammalia,  like  our  moles  and  shrews ;  and  from  this  time 
the  reptiles  become  smaller,  as  if  they  were  kept  down 
and  gradually  destroyed  by  the  higher  animals,  and  the 
•  quadrupeds  become  larger  and  more  powerful ;  till,  in  those 
beds  which  Cuvier  studied  near  Paris,  we  find  the  gigantic 
elephant  and  rhinoceros-like  animals  we  spoke  of  before ; 
while  in  beds  of  about  the  same  age  occur  the  first  bones  of 
monkeys. 

This  is  a  very  rough  sketch  of  the  order  in  which  ani- 
mals are  found  in  the  earth's  crust.  The  lower  kinds  first,  and 
then  gradually  higher  and  higher  forms  as  they,  come  near  to 
our  own  time  ;  and  if  we  could  study  them  more  closely  you 
would  see  that  in  rocks  nearly  of  the  same  age  the  forms 
are  always  very  like  each  other,  while  the  farther  apart  the 
formations  are,  the  more  different  are  the  animals.     It  is  true 


424  NINETEEKTH   CEiVTURY.  pt.  hi. 

that  there  are  very  few  close  Hnks  to  be  found  between  fossil 
animals  ;  but  when  Ave  remember  that  nearly  all  the  rocks  in 
the  earth's  crust  are  made  out  of  others  which  have  been 
destroyed,  it  is  scarcely  wonderful  that  so  few  skeletons 
should  be  found  of  those  that  were  once  buried,  and  it  is 
not  likely  that  many  of  these  would  be  just  the  intermediate 
forms  we  want.  Still  some  have  come  to  light,  for  a  bird- 
reptile  has  been  found  in  the  rocks  of  Kansas,  in  America, 
which  has  a  skeleton  like  a  bird,  but  teeth  and  jaws  like  a 
reptile ;  and  a  reptile  has  been  dug  out  of  the  Stonesfield 
slate  in  England,  which  Mr.  Huxley  says  must  have  hopped 
like  a  bird,  having  legs,  neck,  and  a  bird-like  head,  while  it 
had  nevertheless  teeth  like  a  reptile.  Again,  horses  have 
been  found  in  the  rocks  of  America,  which  have  sepa- 
rate toes,  and  others  in  which  the  toes  are  beginning  to 
grow  together,  showing  how  they  may  have  been  gradually 
altered  into  our  one-toed  horse. 

And  here  again,  those  who  studied  fossil  animals  asked 
why  these  forms  should  succeed  each  other,  gradually  pas- 
sing on  into  the  living  forms  of  our  own  day,  which  are  all 
slightly  altered  copies  of  these  fossils  of  the  rocks  ? 

How  can  Plants  and  Animals  have  become  altered  ? — 
It  was  questions  such  as  these  which  seemed  to  call  for 
answers,  and  to  find  none  except  the  one  proposed  by 
Lamarck  j  namely,  that  the  different  kinds  of  animals  are 
all  desceiided  from  a  few  simple  forms.  If  this  were  so,  then 
it  would  be  quite  natural  that  higher  and  higher  forms  should 
appear  gradually  upon  the  earth,  and  that  the  kinds  most 
alike  should  follow  directly  upon  each  other,  those  which  are 
now  living  being  very  like  their  ancestors  in  the  newest 
formation  in  the  earth's  crust.  It  would  also  help  us  to 
understand  why  animals  of  the  same  class  should  have  the 


CH.  XL.  DARWIN'S  THEORY,  425 

same  bones,  and  why  some  should  have  parts  remaining  in 
their  body  which  are  no  longer  of  any  use  ;  and  lastly,  it 
would  explain  why  naturalists  have  so  much  difficulty  in 
distinguishing  nearly  related  species. 

But  though  these  reasons  made  it  seem  very  likely  that 
all  animals  are  only  different  branches  from  one  stem,  yet 
this  could  only  be  a  mere  speculation  unless  some  one  could 
point  out  what  has  made  them  differ  so  much  from  each 
other.  Lamarck,  as  we  have  seen,  could  not  do  this,  and 
therefore  his  suggestion  was  passed  by ;  and  it  was  not  till 
about  sixteen  years  ago  that  two  naturalists,  Mr.  Darwin  and 
Mr.  Wallace,  discovered  a  law  which  is  certainly  true  in 
itself,  and  which  accounts  for  many  of  the  facts.  Their 
theory,  which  we  must  now  consider,  is  so  new  that  it  has 
been  opposed  on  all  sides,  just  as  the  Copernican  theory  was 
opposed  in  the  sixteenth  century,  the  circulation  of  the  blood 
in  the  seventeenth  century,  and  the  theory  of  combustion, 
which  overturned  phlogiston,  in  the  eighteenth  century.  We 
live  in  the  midst  of  the  discussion  about  the  origin  of  spe- 
cies, and  it  will  only  be  our  great-grandchildren  who  will  be 
able  to  talk  of  the  Darwinian  theory  in  the  way  in  which 
we  talk  of  the  discoveries  of  past  centuries  ;  but  you  ought 
at  least  to  understand  what  this  theory  is,  for  it  forms  an 
era  in  the  history  of  science. 

Darwin's  Theory  that  Natural  Selection  has  caused  the 
various  kinds  of  Plants  and  Animals  to  differ  widely  and 
permanently  from  each  other. — The  theory  of  Natural  Selec- 
tion, or  the  Darwinian  theory  as  it  is  often  called,  has  been 
chiefly  worked  out  by  a  great  living  naturalist,  Mr.  Charles 
Darwin,  who  was  born  in  1809.  When  he  was  only  two-and- 
twenty,  Mr.  Darwin  went  in  her  Majesty's  ship  '  Beagle '  to 
survey  the  coast  of  South  America  and  sail  round  the  globe  j 


426  NINETEENTH  CENTURY.  pt.  hi. 


and  on  his  return  he  wrote  an  account  of  the  geology  and 
natural  history  of  the  countries  he  had  visited.  He  tells  us 
himself  that  even  so  early  as  this  he  noticed  many  facts 
which  seemed  to  him  to  tlirow  light  on  the  difficult  question 
of  the  origin  of  the  different  species  of  plants  and  animals  ; 
and  he  spent  twenty  years  carefully  collecting  in  England  all 
the  knowledge  he  could  upon  the  subject.  But  he  did  not 
publish  it,  for  he  wanted  more  and  more  evidence  ;  and  as 
Newton  waited  sixteen  years  for  more  convincing  proof 
before  he  announced  his  theory  of  gravitation,  so  Mr.  Dar- 
win would  have  delayed  much  longer  than  he  did  if  a 
remarkable  circumstance  had  not  obliged  him  to  speak. 

It  happened  that  while  Mr.  Darwin  was  working  in  Eng- 
land, another  great  naturalist,  Mr.  Alfred  R.  Wallace,  who 
was  then  in  the  Malay  Archipelago,  also  thought  that  he 
had  discovered  the  way  in  which  animals  are  made  to  vary 
in  the  course  of  long  ages.  He  sent  home  a  paper  on  the 
subject,  and,  though  he  had  never  heard  of  Mr.  Darwin's 
theory,  it  was  found  that  he  had  worked  out  the  same 
result,  sometimes  almost  in  the  same  words. 

Sir  C.  Lyell  and  Dr.  Hooker  of  Kew  were  so  much  struck 
with  the  fact  that  these  two  men  had  solved  the  problem 
almost  precisely  in  the  same  way,  that  they  begged  Mr. 
Darwin  to  allow  one  of  his  papers,  written  many  years 
before,  to  be  published  with  Mr.  Wallace's,  and  the  two 
essays  were  read  the  same  evening,  July  i,  1858,  at  the 
Linnsean  Society.  A  year  later,  in  November  1859,  Mr.  Dar- 
win's famous  work,  '  The  Origin  of  Species,'  was  published. 

'  The  Theory  of  Natural  Selection,'  or  the  choosing  out 
by  natural  causes  of  those  plants  and  animals  which  are 
best  fitted  to  live  and  multiply,  rests  upon  a  few  simple  facts 
which  you  can  understand. 


CH.  XL.  DARWIN'S  THEORY.  427 

Firstly,  all  living  beings  multiply  so  rapidly  that  there 
would  be  neither  room  nor  food  enough  upon  the  earth  for 
them  if  they  were  all  to  live  ;  therefore  immense  numbers 
must  die  young,  and  those  will  live  the  longest  and  have 
children  to  follow  them  who  are  best  fitted  for  the  kind  of 
life  they  have  to  lead. 

Secondly,  no  two  living  beings  are  ever  exactly  alike ; 
but  children  always  inherit  some  of  the  characters  of  their 
parents,  so  that  if  any  being  has  a  peculiarity  which  makes 
it  better  fitted  for  its  life,  and  consequently  lives  long  and 
has  a  large  family,  some  of  its  descendants  will  most  likely 
inherit  that  peculiarity. 

Now  it  is  not  difficult  to  understand  that  if  useful 
peculiarities  of  different  kinds  are  handed  down  in  this  way 
from  parent  to  child,  those  who  inherit  them  will  in  time 
begin  to  be  remarkable  for  diff"erent  qualities.  For  example, 
suppose  that  in  a  nest  of  young  birds,  one  with  strong  wings 
lives  and  has  young  because  it  can  fly  far  and  get  food, 
while  another  also  lives  and  has  young  because  its  feathers 
are  dark,  and  the  hawks  cannot  see  it  in  the  grass.  Then 
those  descendants  of  the  strong-winged  bird  which  also 
have  strong  wings,  will  be  most  likely  to  live  on  in  each 
generation,  and  will  pass  on  this  peculiarity  to  their  children; 
while  the  descendants  of  the  dark-coloured  bird  will  also  sur- 
vive in  each  generation  exactly  in  proportion  as  their  plum- 
age is  adapted  to  hide  them ;  and  thus  the  strong-winged 
birds  and  the  dark-winged  birds  will  in  time  become  very 
different  from  each  other.  This  is  roughly  the  theory  of 
'  Natural  Selection  ; '  that  nature  allows  only  those  animals 
to  live  which  in  some  way  escape  the  dangers  which  threaten 
their  neighbours,  and  thus  in  time  the  race  becomes  altered 
to  suit  the  life  it  has  to  lead. 


428  NINETEENTH  CENTURY.  pt.  hi. 

There  is  only  one  difficulty.  It  is  clear  that  the  strong- 
winged  birds  must  not  pair  with  the  dark- winged  birds,  or 
otherwise  both  peculiarities  would  come  out  in  the  young 
birds,  and  the  two  kinds  would  no  longer  remain  distinct. 
And  this  is  the  one  stumbling-block  in  the  theory ;  we 
have  never  yet  been  able  to  trace  out  two  varieties  of  an 
animal  which  have  become  so  different  that  they  do  not  pair 
together.  You  should  fix  this  difficulty  firmly  in  your  mind, 
because  it  is  almost  the  only  real  one  we  shall  meet  with. 
Mr.  Darwin's  answer  to  it  is,  that  we  have  only  watched 
plants  and  animals  for  such  a  short  time,  and  even  then  not 
with  this  idea  in  our  minds,  so  that  we  are  not  likely  to 
have  found  a  case  to  help  us.  It  has  indeed  been  observed 
that  animals,  if  left  free  to  choose,  do  often  pair  with  those 
which  resemble  themselves,  and  do  in  some  cases  show  a 
dislike  to  those  that  differ;  still  this  is  not  proved  to  be 
always  the  case,  and  it  must  be  acknowledged  to  be  a 
difficulty. 

Selection  of  Animals  by  Man. — But  now  setting  this 
aside,  let  us  see  what  proof  there  is  that  animals  vary,  and  that 
they  can  be  picked  out,  so  that  any  peculiarity  may  become 
stronger  in  each  succeeding  generation.  The  best  instance  is 
in  pigeons.  All  our  pigeons  come  from  the  common  wild 
rock-pigeon;  and  the  way  in  which  all  our  pouters,  fan-tails, 
barbs,  and  other  pigeons  have  been  produced,  is  by  merely 
picking  out  from  the  young  ones  those  which  had  either  large 
crops,  or  wider  tails,  or  longer  beaks,  and  pairing  them  to- 
gether, so  that  the  young  birds  had  these  peculiarities  still 
more  strongly.  The  same  thing  is  true  of  our  different  kinds 
of  oxen,  sheep,  horses,  and  fowls ;  so  we  see  clearly  that 
different  varieties  can  be  produced  by  choosing  out  parti- 
cular animals.     Man   does   this   quickly,  because   he  only 


CH.  XL,  NATURAL  SELECTION.  429 


attends  to  one  peculiarity,  which  interests  him ;  but  nature 
does  it  very  slowly,  because  no  animal  can  live  unless  every 
part  of  it  is  fitted  for  its  life  better  than  in  those  which  are 
killed  off. 

Selection  by  Natural  Causes. — Now  Mr.  Wallace  has 
calculated  that  one  pair  of  birds  having  four  young  ones 
a  year,  would,  if  all  their  children,  grandchildren,  and  great- 
grandchildren, lived  and  paired,  produce  about  two  thou- 
sand million  descendants  in  ffteen  years.  And  Mr.  Huxley 
tells  us  that  a  single  plant  producing  fifty  seeds  a  year  would 
if  unchecked  cover  the  whole  globe  in  nine  years,  and  leave 
no  room  for  other  plants. 

It  is  clear,  therefore,  that  out  of  these  numbers  millions 
must  die  young,  and  it  is  only  the  most  fitted  in  every  way 
that  can  live  and  multiply.  One  example  from  Mr.  Darwin's 
book  will  show  you  how  complicated  the  causes  are,  which 
determine  what  particular  kinds  shall  flourish.  He  tells  us 
that  the  heartsease  and  the  Dutch  clover,  two  common 
plants,  can  only  form  their  seeds  when  the  pollen  is  carried 
from  flower  to  flower  by  insects.  Humble-bees  are  the  only 
insects  which  visit  these  flowers,  therefore  if  the  humble-bees 
were  destroyed  in  England  there  would  be  no  heartsease  or 
Dutch  clover. 

Now  the  common  field-mouse  destroys  the  nests  of  the 
humble-bee,  so  that  if  there  are  many  field-mice  the  bees 
will  be  rare,  and  therefore  the  heartsease  and  clover  will  not 
flourish.  But  again,  near  the  villages  there  are  very  few  field- 
mice,  and  this  is  because  the  cats  come  out  into  the  fields 
and  eat  them  ;'  so  that  where  there  are  many  cats  there  are 
few  mice  and  many  bees,  and  plenty  of  heartsease  and  Dutch 
clover.  Where  there  are  few  cats,  on  the  contrary,  the  mice 
flourish,  the  bees  are  destroyed,  and  the  plants  cease  to  bear 


430 


NINETEENTH  CENTURY.  pt.  ill. 


seed  and  to  multiply.  And  so  you  see  that  it  actually  de- 
pends upon  the  number  of  cats  in  the  neighbourhood  how- 
many  of  these  flowers  there  are  growing  in  our  fields. 

But  now  let  us  suppose  for  a  moment  that  among  the 
field-mice  there  are  some  whose  skin  has  a  slightly  peculiar 
smell,  so  that  the  cats  do  not  eat  them  when  they  can  find 
others.  Clearly  these  mice  would  live  longest  and  have  most 
offspring  \  and  of  these  again,  those  with  strong-smelling  skins 
would  live ;  and  so  after  a  time  a  new  race  of  mice  would 
arise  which  would  be  independent  of  the  cats,  and  the  bees 
would  have  a  poor  chance  of  living,  and  consequently  the 
flowers  of  bearing  seeds. 

But  this  might  in  the  end  give  rise  to  quite  a  new  race 
of  plants,  for  it  is  believed  that  some  moths  would  visit  the 
clovers,  only  as  Mr.  Darwin  points  out,  they  are  not  heavy 
enough  to  weigh  down  the  petals  of  the  flowers  so  as  to 
creep  inside  them.  But  as  no  two  flowers  are  ever  exactly 
alike,  it  is  very  likely  that  the  petals  of  some  blossoms  will 
droop  a  little  more  than  in  the  others,  and  so  if  the  bees 
became  scarce,  these  blossoms  with  drooping  petals  might 
live  on,  because  the  moths  could  creep  into  them  and  carry 
their  pollen  from  flower  to  flower ;  and  thus  a  new  race  of 
clover  with  drooping  petals  might  spring  up  independent  of 
the  cats,  the  mice,  and  the  bees,  and  would  become  a  new 
species. 

You  must  especially  notice  in  this  imaginary  example 
that  it  is  only  useful  variations  which  can  be  passed  on 
from  generation  to  generation.  If  the  smell  of  the  mice 
(which  would  probably  come  from  some  peculiarity  in  the 
pores  of  the  skin)  did  not  preserve  them  from  the  cats,  the 
strong- smelling  mice  would  not  live,  and  a  peculiar  race 
would  not  arise ;  in  the  same  Avay,  if  the  drooping  leaves  of 


CH   XL.  NATURAL  SELECTION,  431 


the  clover  did  not  enable  the  moths  to  enter,  those  plants 
would  die  out  like  the  others.  And  this  is  one  of  the  most 
striking  facts  which  Mr.  Darwin  has  pointed  out ;  namely, 
that  no  variation  will  continue  and  increase  from  generation 
to  generation  unless  it  is  useful  to  the  plant  or  animal  which 
possesses  it ;  so  that  if  this  theory  be  true,  every  beautiful 
colour  which  we  admire  in  animals  and  plants,  every  minute 
detail  in  their  form  and  structure,  is  not  only  to  be  admired 
for  its  beauty,  but  because  it  is  an  evidence  of  that  won- 
derful harmony  of  nature  which  keeps  every  part,  however 
insignificant,  exactly  fitted  to  do  its  work  in  the  one  great 
scheme  of  creation. 

Difficulties  in  Natural  History  explained  by  Natural 
Selection. — And  now,  if  we  adopt  Mr.  Darwin's  explanation, 
you  will  see  how  St.-Hilaire  and  Cuvier  could  both  be 
right  when  the  one  said  that  all  animals  are  formed  on 
one  plan,  and  the  other  that  each  part  of  an  animal  is 
exactly  fitted  to  work  harmoniously  with  the  rest  of  its 
body.  For  if  animals  have  been  gradually  altered  the  one 
from  the  other,  it  is  natural  they  should  all  be  made  on 
one  plan ;  as,  for  instance,  if  the  ancestor  of  the  bat,  millions 
of  years  ago,  was  also  the  ancestor  of  those  animals  out  of 
which  the  horse  has  come,  then  the  bones  of  the  bat's  wing 
may  well  be  similar  to  those  of  the  horse ;  while,  on  the 
other  hand,  if  no  variation  can  become  fixed,  and  develope 
into  important  parts  or  organs  unless  it  is  useful,  it  is  clear 
that  all  the  parts  of  an  animal  must  have  been  gradually 
modified  so  as  to  fit  each  other  and  to  work  in  the  best  pos- 
sible way  for  its  well-being.  Again,  it  explains  why  the  living 
animals  in  a  country  should  be  of  the  same  class,  though 
slightly  different  from  those  found  fossil  in  the  earth.  For 
if  in  Australia  the  ancestors  were  pouched  animals,  it  must 


432  NINETEENTH  CENTURY.  ft.  hi. 

take  a  very  long  time  before  their  descendants  could  be  any- 
thing else,  although  they  might  begin  to  differ  in  many 
points. 

Lastly,  it  enables  us  to  understand  why  we  find  the  lower 
forms  of  life  in  the  oldest  rocks,  and  why  gradually,  as 
animals  multiplied  and  the  struggle  for  life  became  greater, 
more  and  more  complicated  forms  should  arise,  from  the 
improvement  and  inheritance  of  specially  useful  parts ;  so 
that  the  higher,  animals  have  a  greater  number  of  different 
parts  to  perform  different  actions,  just  as  a  civiHzed  country 
with  a  great  number  of  skilled  people  in  it,  has  men  of 
different  trades  and  professions,  one  to  brew  and  one  to 
bake,  one  to  dig  the  ground,  and  to  grow  cotton  and  flax, 
and  another  to  weave  them  into  garments. 

This  will  give  you  a  very  small  glimpse  of  some  of  the 
difficulties  which  are  explained  by  the  theory  of  natural 
selection.  The  subject  is  so  difficult  to  understand  tho- 
roughly, that  you  must  not  expect  to  have  more  than  a 
slight  notion  of  it,  and  must  be  content  for  the  present  with 
knowing  that  our  greatest  living  naturalists,  who  have  made 
a  careful  study  of  living  and  fossil  animals  and  plants,  all 
believe  it  to  be  true. 

And  as  this  is  so,  it  is  extremely  foolish  to  be  prejudiced 
against  it,  as  some  people  are,  by  the  idea  that  animals 
formed  in  this  way  can  be  less  God's  creation  than  if  they 
were  made  in  any  other  way.  The  whole  history  of  science 
teaches  us  that  men,  in  all  ages,  have  constantly  taken  false 
alarm  when  it  has  been  shown  that  God's  ways  are  not  our 
ways,  and  that  the  universe  is  governed  by  far  wider  and 
more  constant  laws  than  we  had  imagined  in  our  little 
minds.  But  in  the  same  way  as  the  planets  are  none  the 
less  held  in  God's  hand  because  we  now  know  that  it  is  by 


CH.  XL.  CONCLUDING  REMARKS.  433 

the  law  of  gravitation  that  He  governs  their  movements,  so 
every  plant  and  animal  must  be  equally  His  creation,  in 
whatever  way  they  have  been  developed.  Above  and  be- 
yond all  these  laws  which  we  can  trace,  there  remains  ever 
the  One  Great  and  Supreme  Creator  whom  Anaxagoras  wor- 
shipped instead  of  the  heathen  gods  of  Greece  (see  p.  14), 
when  his  fellow-countrymen  condemned  him  as  an  unbe- 
liever because  he  believed  not  in  many,  but  in  One  God. 

A  humble,  earnest  spirit  seeking  knowledge  must  indeed 
find  in  modern  science  a  deep  revelation  of  the  Unity  and 
Unchangeableness  of  the  Creator.  Instead  of  many  widely 
different  sciences  standing  each  alone,  which  the  great  men 
of  earlier  centuries  worked  out,  we  are  beginning  to  be  able 
to  discern  one  constant  power  working  through  them  all ; 
while  still  new  fields  of  discovery,  such  as  that  which 
spectrum  analysis  has  only  lately  opened  out  to  us,  help  us  to 
bear  in  mind  how  little  we  know,  and  how  much  more  vast 
than  anything  that  we  can  imagine,  must  be  the  great  scheme 
of  Creation  which  is  being  worked  out  around  and  within  us. 

Concluding  Remarks. — We  have  now  arrived  at  the  end 
of  our  history,  for  a  summary  of  the  science  of  the  nineteenth 
century  is  manifestly  impossible.  The  subject  has  become 
too  vast  to  be  dealt  with  in  a  short  sketch,  even  if  the  limits 
of  this  little  volume  were  not  already  reached.  Besides,  as 
we  have  not  mentioned  the  work  of  living  men,  except  in 
cases  such  as  those  of  Kirchhoff  and  Darwin,  where  it  was 
impossible  to  be  avoided,  we  have  not  really  examined  the 
science  of  this  century,  but  only  very  small  portions  of  it. 
•  We  can  therefore,  in  conclusion,  only  try  to  understand  the 
tendency  of  the  science  of  our  day  as  compared  with  that  of 
earlier  centuries. 

20 


434 


NINETEENTH  CENTURY.  pt.  hi. 


The  work  of  the  sixteenth  century,  as  we  saw  (p.  82), 
was  to  overcome  that  blind  worship  of  authority  which  had 
sprung  up  during  the  Dark  Ages,  and  which  is  the  greatest 
enemy  to  true  knowledge. 

In  the  seventeenth  century  the  march  of  scientific 
discovery  began  with  Galileo,  and  advanced  slowly  but 
triumphantly  through  many  dangers  and  difficulties,  till 
it  ended  in  the  grand  generalizations  of  Newton.  This 
was  the  first  great  era  of  modern  science,  especially  of 
astronomy  and  physics,  though  biology  also  made  a  great 
stride  when  Harvey  demonstrated  the  circulation  of  the 
blood. 

The  eighteenth  century  continued  the  same  work  of 
patient  enquiry,  completing  the  harmony  of  astronomy  by 
bringing  the  observed  movements  of  the  planets  under 
Newton's  law  of  gravitation ;  founding  chemistry  upon  a 
firm  basis  of  careful  experiment ;  creating  the  sciences  of 
zoology  and  botany,  by  establishing  true  systems  of  classi- 
fication ;  discovering  the  hitherto  almost  unknown  force  of 
electricity  j  and  reading  in  the  crust  of  the  earth  the  history 
of  the  past  ages  of  our  planet. 

And  so  when  the  nineteenth  century  opened,  men  found 
themselves  with  an  immense  mass  of  known  facts  and- 
careful  experiments,  which  had  been  accumulated  during 
the  last  two  centuries,  and  which  were  very  difficult  to  deal 
with,  because  it  had  become  almost  impossible  for  any  single 
mind  to  grasp  them  all.  The  scientific  men  of  our  century 
have  therefore  become  divided  into  two  great  classes.  On  the 
one  hand  men  have  devoted  themselves  to  special  sciences, 
and  even  to  special  branches  of  a  science,  so  that  a  man  will 
often  spend  his  whole  life  in  the  study  of  one  department  of 
chemistry  or  physics,  or  in  investigating  one  little  group  of 


CH.  XL.  CONCLUDING  REMARKS.  435 

insects  j   and  in  this  way  discoveries  of  great  value  have 
been  made. 

On  the  other  hand  great  minds  among  us  have  taken  up 
the  separate  facts  collected  by  specialists,  and  have  woven 
the  whole  of  physical  science  into  one  grand  scheme.  Such 
men  as  Faraday,  Helmholtz,  Sir  W.  Thomson,  and  Grove, 
together  with  many  others,  have  done  their  part  in  this  work, 
so  that  now  all  the  various  physical  forces  have  been  shown 
to  be  probably  phases  of  one  great  force,  appearing  under 
many  forms.  For  the  future  no  one  physical  force  can  be 
studied  as  if  it  existed  by  itself  alone,  for  each  is  shown  to 
arise  out  of  and  to  pass  into  others.  Heat,  electricity,  mag- 
netism, chemical  affinity,  motion — all  are  related  to  each 
other,  and  we  cannot  call  any  one  of  them  the  ruler  over  the 
rest.  Like  the  colours  on  the  soap-bubble,  they  each  take 
their  turn  in  appearing  and  disappearing,  according  to  the 
conditions  under  which  they  arise.  Their  relations  are 
almost  infinitely  complex,  and  we  have  still  much  to  learn 
about  them ;  but  the  grand  fact  that  they  pass  the  one  into 
the  other  without  loss  of  energy  has  been  demonstrated  in 
our  century  ;  and,  under  the  names  of  '  the  conservation  of 
energy,'  and  '  the  correlation  of  the  physical  forces/  is  one 
of  the  greatest  results  of  modem  science. 

The  same  tendency  may  be  seen  in  the  study  of  those 
sciences  which  relate  to  life.  Here  again  modern  investiga- 
tion links  together  the  scattered  observations  of  ages,  and 
unites  them  all  in  the  theory  of  '  evolution,'  or  the  gradual 
unfolding  of  nature ;  a  theory  which  has  been  worked  out 
in  all  its  details  by  Herbert  Spencer,  one  of  our  greatest 
living  thinkers.  In  astronomy,  indeed,  we  already  catch 
a  glimpse  of  this  law  in  the  probable  formation  of  the 
heavenly  bodies  out  of  gaseous  star-matter  ;  and  in  the  or- 


436  NINETEENTH  CENTURY.  pt.  hi. 

ganic  world  we  find  it  even  more  firmly  held  by  scientific 
men  in  the  belief  that  all  the  many  forms  of  plant  and 
animal  life  have  been  unfolded  out  of  a  few  simple  forms, 
just  as  the  stem,  the  leaf,  and  the  flower  aire  evolved  out  of 
a  simple  seed. 

Whether  this  theory  is  true  or  not,  it  must  be  the  work 
of  many  generations  to  prove,  for  the  history  of  science 
teaches  us  that  nothing  but  truth  can  stand  the  test  of  long 
investigation,  while  no  power  or  authority  can  resist  in  the 
end  that  which  is  true.  The  mistaken  theory  of  phlogiston 
did  its  work  in  gathering  together  many  scattered  facts  in 
chemistry,  and  then  died  a  natural  death  when  the  discovery 
of  oxygen  threw  more  light  upon  the  subject ;  while  no 
authority  or  persecution  could  suppress  the  true  theory  that 
the  earth  moves  round  the  sun. 

It  is  of  great  importance  that  we  should  all  learn  this 
lesson,  to  have  faith  in  the  invincible  power  of  truth  j  for  it 
would  almost  seem  as  if  all  the  experience  of  past  centuries 
had  hardly  yet  convinced  us.  We  still,  like  the  Aristotelians 
and  the  judges  of  the  Inquisition,  often  make  hasty  and 
ignorant  assertions,  and  try  rather  to  prop  up  by  authority 
that  which  we  believe,  than  to  enquire  earnestly  whether  it 
is  true.  Yet  every  page  in  the  History  of  Science  teaches 
the  contrary  lesson.  So  much  as  is  true  in  any  belief  will 
stand  because  it  is  true;  while  that  which  is  mistaken  will 
fade  away  before  earnest  and  impartial  examination.  Our 
part  is  to  endeavour,  like  the  great  men  of  whom  we  have 
been  reading,  to  open  our  eyes  to  the  laws  which  surround 
us,  and  which  are  only  hidden  from  us  by  our  ignorance. 
And  from  whatever  source  we  derive  our  knowledge  we 
must  remember  that  it  is  very  little  after  all,  and  be  ready  at 
all  times  to  exanmze  new  facts,  even  though  they  may  seem 


CH.  XL.  CONCLUDING  REMARKS.  437 

to  upset  some  of  our  favourite  opinions;  for  unless  we 
know  everything,  it  is  certain  that  we  must  at  times  find 
that  we  have  been  mistaken. 

Those  who  will  labour  in  this  spirit  of  seeking  the  truth 
for  itself  will  find  their  reward  in  the  ever-increasing  delight 
they  will  feel  in  studying  God's  works,  and  in  the  assurance 
which  they  will  meet  with  at  every  step,  that  nothing  can 
happen  except  under  the  guidance  of  His  laws.  True 
science,  like  true  religion,  leads  to  an  entire  and  childlike 
dependence  upon  the  Invisible  Ruler  of  the  universe.  It 
makes  us  eager  to  study  God's  laws,  that  we  may  live  in 
accordance  with  them,  and  diminish  some  of  the  gross 
ignorance  which  now  prevails  ;  while  at  the  same  time  it 
leads  even  the  most  instructed  to  feel  how  extremely  limited 
our  knowledge  is,  and  that  we  are  after  all  like  inexperienced 
children,  dependent  upon  the  love  and  power  of  our  Maker 
to  bring  us  safely  out  of  darkness  into  light. 


Chief  Works  consulted,  — Darwin's  '  Origin  of  Species  ; '  Wallace's 
'Natural  Selection;'  Huxley's  'Lectures  to  "Working  Men;'  Lyell's 
'Principles  of  Geology.' 


CHRONOLOGICAL     TABLES 


OF    THE 


RISE    AND    PROGRESS    OF    THE    VARIOUS 
I  BRANCHES    OF    SCIENCE 


440 


CHRONOLOGICAL    TABLE. 


SCIENCE   OF   THE    GREEKS. 

FROM  B.C.  639  TO  A.D.   2CX). 

TJte  dates  of  this  table  refer  to  the  years  in  ivhich  each  particular  step  in  advatice  was 
made;  but  iip  to  the  end  of  the  Middle  Ages  they  nitist  be  regarded  as  merely 
approximative. 


Astronomy. 


B.C. 

600.  Thales  marks 
out  solstices  and 
equinoxes,  p.  8. 

570.  Anaximan- 
der  —  The  sun- 
dial ;  the  phases 
of  the  moon,  p.  9. 

i50o.      Pythagoras 

—  The  earth 
moves ;  morn- 
ing and  even- 
ing star  the 
same,  p.  11. 

450.    Anaxagoras 

—  Nature  of 
sun  and  moon ; 
eclipses  ;  move- 
ments of  the 
planets,  p.  13. 

400.  Democrituson 
Milky  Way,  p.  15. 

360.  Eudoxus  on 
movements  of 
the    planets,   p. 

357.  Aristotle  on 
occultation  of 
Mars  ;  asserts 
that  the  earth  is 
round,  p.  16. 
Ecliptic  and  Zo- 
diac understood 
by  the  Greeks, 
p.  18. 

Aristarchus. 
Earth  moves 
round  the  sun ; 
obliquity  of 
ecliptic;  rota- 
tion of  earth 
on  its  axis,  p.  20. 

130.  Hipparchus 
on  precession  of 
the  equinoxes  ; 
calculates  ec- 
lipses, p.  29. 


A.  D.  100.  Ptole- 
my founds  the 
Ptolemaic  sys- 
tem, p.  32. 


Physics  and 
Mechanics. 


260.  Euclid  on 
light  travelling 
in  straight  lines, 
p.  21. 

250.  Archimedes 
on  the  lever ; 
Hiero's  crown 
and  specific  gra- 
vity ;  screw  of 
Archimedes,  pp. 
22-25. 

120.  Hero's  en- 
gine, p.  245. 


Chemistry. 


Greeks  knew  how 
to  extract  iron, 
mercury,  and 
other  metals 
from  the  ore  ; 
and  make  co- 
lours out  of 
earths,  p.  40. 


Physical 

Geography  and 

Geology. 


570.  Anaximan- 
der  makes  a 
map  of  the 
known  world,  p. 
10. 

500.  Pythagoras 
on  changes  of 
land  and  sea ; 
on  earthquakes, 
voicanos,  and 
p  e  t  r  i  f  yi  ng 
springs,  pp.  11- 


230.  Eratosthe- 
nes lays  down 
first  parallel  of 
latitude  ;  mea- 
sures circumfer- 
ence of  the 
earth ;  studies 
mountai  n 
chains,  pp.  27- 
29. 


A.D.  100.  Ptole- 
my on  geo- 
graphy, p.  23. 

Strabo  on  earth- 
quakes and  vol- 
canoes, p.  33. 


Biology. 


390.  Hippocrates 
father  of  medi- 
cine ;  separates 
medicine  from 
the  priesthood, 

p.  15. 

341.  Aristotle 
founder  of  zoo- 
logy ;  studies 
the  nature  of 
plants  and  ani- 
mals, p.  16. 

340.  Theophras- 
tus  first  bota- 
nist, p.  17. 

Erasistratus  and 
Herophilus  the 
first  anato- 
mists ;  they 
study  brain, 
muscles,  and 
nerves,  p.  26. 


A.D.  160.  Galen, 
physician, 
studies  nerves 
and  arteries ; 
works  out  a 
theory  of  medi- 
cine, p.  33. 


CHRONOLOGICAL   TABLE. 


441 


SCIENCE   OF   THE   MIDDLE   OR  DARK  AGES. 

FROM  A.D.   700  TO    1500. 


The  Arabs  great 
astronomers,  but 
mix  up  astrono- 
my with  astro- 
logy, p.  45- 


Astronomy. 


goo.  Albategnius 
calculates  the 
length  of  the 
year,  p.  45. 

1008.  Ebn  Junis 
draws  up  astro- 
nomical tables, 
p.  46. 


Physics  and 
Mechanics. 


(900.  Ben  Mtisa 
on  algebra  and 
nutnerals). 

(1000.  Gerhertht- 
trodtices  A  rabic 
ntimerals  into 
Euro;pe\ 

1030.  Alhazen  on 
refraction  of 
light ;  on  atmo- 
spheric  reflec- 
tion ;  on  mag- 
nifying glasses, 
pp.  46-50. 


1 240.  Roger  Ba- 
con and  Vitellio 
on  cause  of  the 
rainbow,  p.  53. 

1302.  Flavio  Gio- 
ja  invents  the 
mariner's  com- 
pass, p.  53.    _ 

1438.  Invention 
of   printing,   p. 

55- 
1480.  Leonardo 
da  Vinci  makes 
water-mills  and 
river-locks,  p. 
58. 


Chemistry. 


800.  Marcus 
Grsecus  makes 
gunpowder,  p. 
42. 

Arabian  alche- 
mists ;  gases 
called  'spirit,' 
p.  41. 

)o.  Geber  the 
founder  of  che- 
mistry ;  distilla- 
tion and  sub- 
limation ;  makes 
nitric  and  sul- 
phuric acid  ; 
discovers  t  hat 
heating  a  metal 
adds  to  its 
weight,  pp.  43- 
45- 


1240.  Roger 
Bacon's  experi- 
ments on  air ; 
he  makes  gun- 
powder;  his 
'  Opus  Majus.' 
p.  52. 


Physical 

Geography  and 

Geology. 


80.  Avicenna,  a 
famous  writer 
on  minerals,  p. 
50. 


1492.  Columbus 
discovers  Ame- 
rica, p.  36. 

1497.  Vasco  di 
Gama  sails 
round  the  Cape 
of  Good  Hope ; 
sees  the  south- 
em  stars,  p.  57. 


Biology . 


Arabs  learn  medi- 
cal science  from 
Jews  and  Nes- 
torians,  p.  40. 

700  to  800.  Medi- 
cal schools  of 
Bagdad  and  Sa- 
lerno flourish, 
p.  40. 

Arabs  devote 
themselves  to 
medicine  be- 
cause dissection 
is  forbidden  by 
the  Koran,  p. 
40. 

920.  Medical 
school  of  Cor- 
dova founded, 
p.  40. 


1030.  Alhazen  on 
nature  of  sight ; 
why  we  do  not 
see  double  with 
two  ej'-es,  pp. 
47-49- 


442 


CHRONOLOGICAL   TABLE. 


RISE  OF   MODERN   SCIENCE. 

FROM  A.D.    1 5 19  TO   1604. 


Astronomy. 

Physics  and 
Mechanics. 

Chemistry. 

Physical 

Geography  and 

Geology. 

Biology. 

1519.   Magellan's 

1530.  Paracelsus, 

ship  sails  round 

chemist  and  al- 

the world,  p.  67. 

1542.      Vesalius 

1543.  Copemican 

chemist,  sepa- 

refutes   Galen  ; 

system  publish- 

rates out   gold 

his  anatomical 

ed,  p.  65. 

1560.     Baptiste 
Porta  invents 
the  camera  ob* 
scura,  p.  74. 

by  means  of 
aquafortis,      p. 
72. 

1565.     Gesner  on 

drawings,  p.  66. 

1548.      Fallopius 
on  anatomy,  p. 
68. 

1551.     Gesner, 
first  _  zoological 
cabinet     and 
botanical    g  a  r- 
den,  p.  68. 

1560.    Eustachi- 
us.  — Eustach- 
ian tube,  p.  68. 

1560.      Porta   on 
structure  of  the 
eye,  p.  76, 

1565.      Gesner 's 

157  5-     Tycho 

mineralogy  and 

'History   of 

Brahe's     obser- 

fossil shells,  p. 

Animals,'  p.  69 ; 

vatory  on  Huen 

70. 

his     classifica- 

island;    Tycho- 

tion  of  plants. 

nic  system,    p. 
78. 
1576.      Tycho  in 

p.  70. 

Bohemia,  p.  79. 

1580.     Porta's 
engine,  p.  246. 

1580.     Palissy, 
the   potter,   in- 

1583.    Galileo  on 

sists  that  fossil 

1583.     Caesal- 

the  pendulum. 

shells  were  once 

pinus    classifies 

P-  79-        ^     . 

real   shells,    p. 

plants  by  their 

1589.     On  falhng 

215. 

flowers  and 

bodies,  p.  80, 

seeds,  p.  71. 

1592.    On  motion 

of  heavy  bodies. 

- 

p.  82. 

1592.      Stevinus 

1594.    Kepler  be- 

on statics,  p.  82. 

gins  to  study  the 

planets,  p.  p5. 

1597.      He  joins 

Tycho    in    Bo- 

hemia, p.  9S._ 

1599.  Rudolphine 

tables  begun,  p. 

79- 
1600.     Bruno 

1600.    Kircher  in- 

1603.    Fabriclus 

burnt  at  the 

vents  the  magic 

discovers  valves 

Stake,  p.  83. 

lantern,  p.  76. 
1600.      Gilbert 
makes  experi- 
ments on  e  1  e  c- 

in  veins,  p.  110. 

1604.      Kepler  on 

formation  of 

images    on    the 

tricity,  p.  77. 

retina,  p.  96. 

CHRONOLOGICAL    TABLE. 


443 


PROGRESS    OF    MODERN    SCIENCE. 

FROM  A.D   1609  TO   1 642. 


Astronomy. 


1609.  Galileo 
discovers  secon- 
dary light  of  the 

.  moon ;  Jupiter's 
moons  ;  phases 
of  Venus,  pp. 
89-92. 

1609.  Kepler's 
two  first  laws, 
pp.  97-99. 

161 1.  Galileo  ob- 
serves sun-spots 
and  proves  ro- 
tation of  sun  on 
its  axis,  p.  92. 

i6i8.  Kepler's 
third  law,  p. 
100. 


Physics  and 
Mechanics. 


1628.  Kepler  com- 
pletes Rudol- 
phine  tables; 
and  foretells 
transits  of  Venus 
and    Mercury, 

P-  157- 
I  6  3 1.     Gassendi 
observes  transit 
of  Mercury,  p. 

157- 

1632.  Galileo  s 
system  of  the 
world ;  his  re- 
cantation, p.  93. 

1639.  Horrocks 
observes  transit 
of  Venus,    p. 

157- 
1642.     Death  of 
Galileo    and 
birth    of   New- 
ton, pp.  64-147. 


1609.  Invention 
of  the  telescope, 
p.  87  ;  Galileo's 
telescope,  p.  89. 


1611.  Kepler's 
telescope,  p.  97. 

1615.  Solomon 
Caus'  engine, 
p.  246. 

1620.  Drebbel, 
alcohol  thermo- 
meter, p.  120. 

620.  Bacon's 
'Novum  O  r- 
ganum,'  p.  103 ; 
Bacon  suggests 
that  heat  may 
be  a  movement, 

P-  330-      , , . 

1621.  Snellius 
discovers  law 
of  refraction,  p. 
106. 

X625.  De  Domi- 
nis  explains  the 
rainbow,  p.  164. 


1637.  Descartes 
on  light  and  re- 
fraction,    pp. 

107-165. 


Chemistry. 


1624.  Van  Hel- 
mont  introduces 
the  term  gas,  p. 
72. 


Physical 

Geography  and 

Geology. 


Biology. 


1619.  Harvey 
discovers  circu- 
lation of  the 
blood,  pp.  iio- 
114. 


622.  Asellius 
discovers  lac- 
teals,  114. 


444 


CHRONOLOGICAL   TABLE. 


PROGRESS   OF   MODERN   SCIENCE. 

FROM    A.D.    1644    TO    1670. 


Astronomy. 

Physics  and 
Mechanics. 

Chemistry. 

Physical 

Geography  and 

Geology. 

Biology. 

1644.    Torricelli 

invents  the  ba- 

(1645.     First 

rometer,  p.  116. 

7nee tings  of 

, 

1646.      Pascal 

Royal  Society, 

proves    the 

p.  124.) 

1647.      Pecquet 

weight    of   air. 

on  the  thoracic 

p.  119. 

duct,  p.  114. 
1649      Riidbeck 

1650.     Guericke 

discovers  lym- 

invents the  air- 

phatics,  p.  115. 

pump  :  Magde- 

1656.      Malpighi 

burg    hemi- 

professor of  me- 

spheres :  first 

dicine    at    Bo- 

electrical   m  a  - 

logna,  p.  138. 

chine,    p.    121- 

123. 

1658.     Huyghens 

1659.     Huyghens 

on  cycloidal 

discovers  Sa- 

pendulums,    p. 

turn's  ring,  and 

174. 

one  satellite,  p. 

I  661.    Poyle's 

1661.     Malpighi 

174, 

law  of  compres- 

(1662.   Acadetnie 

uses  microscope 

sion  of  gases,  p. 

des  Sciences 

to  examine  air- 

128. 

founded,    p. 
126.) 

cells  of  the 
lungs ;  discovers 

1666.    Newton 

M  alpighian 

on    method  of 

layer  ;  studies 

fluxions;  first 

anatomy  of  in- 

idea of  gravita- 

sects,  pp.    137- 

tion,     pp,    '•41- 

139- 

150. 

1663.      Marquis 
of    Worcester's 
engine,  p.  246. 

1666-1671.    New- 
ton on    disper- 
sion   of   light, 
proves  its'  com- 
pound    nature, 
pp.  166-169. 

1665.     Hooke  on 
use   of    air    in 
combustion,    p. 
130. 

1665.    Boyle's  ex- 
periments on 
air,  p.  130. 

1669.     Steno  on 
fossils  and  petri- 
factions, p.  215. 

1663-1666.  Jour- 
neys of  Ray  and 
Willughby,  p. 
143- 

1670.     First  mer- 

1670.     M  a  y  0  w 

1670.     Scilla  on 

1670.      M  a  y  0  w 

curial    thermo- 

discovers   '  fire- 

fossils  of  Cala- 

on   respiration, 

meter,  p.  120. 

air,'  and  shows 
it  is   used   in 
burning,  p.  131. 
1670.      Beecher 
proposes  theory 
of  'phlogiston,' 
P-  1C35- 

bria,  p.  216, 

P-  134. 

i 


CHRONOLOGICAL   TABLE. 


445 


PROGRESS   OF   MODERN    SCIENCE. 

FROM    A.D.     1674    TO    1 732. 


Astronomy. 


1676.  Halley  ob- 
serves transit  of 
Mercury,  p. 
158. 


1682.  Newton 
works  out  and 
publishes  the 
law  of  gravita- 
tion,   pp.    150- 

155- 

1682.  Halley 
foretells  the  re- 
turn of  a  comet, 
p.  162. 

1687.  Newton's 
'  P  r  in  c  i  p  i  a ' 
p  u  b  1  i  s  h  e  d,  p. 
153- 

691.  Halley's 
method  of  mea- 
suring the  sun's 
distance  by  the 
transit  of  Venus, 
p.  158. 


Physics  and 
Mechanics. 


1676.  Roemer 
measures  velo- 
city of  light,  p. 
172. 

1678.  Huyghens 
proposes  undu- 
latory  theory  of 
light;  law  of 
double  refrac- 
tion, p,  175-179' 


1690.  Papln's 
heat-engine,  p. 
246. 


r722.  Graham  on 
shifting  of  mag- 
netic needle,  p. 

355-  ^     „ 
1727.   Bradley  on 

nutation       and 

aberration,      p. 

265. 


Chemistry. 


Physical 

Geography  and 

Geology. 


Biology^ 


1682.  Picart 
measures  the 
size  of  the  earth, 
p.  150. 


598.   Savery  s 
heat-engine,   p. 
246. 
1705.     Newco- 
men's  engine, 
p.  246. 


1729.  C.  More 
Hall  on  disper- 
sion of  light  in 
flint  and  crown 
glass,  p.  169. 

1732.  Du  Faye 
on  electricity, 
p.  254. 


1701.  Boerhaave 
founder  of  or- 
ganic chemis- 
try, pp.  190-194. 

1718.  Hales'  ex- 
periments on 
gases,  p.  226. 


1729.  S  t  a  h  1 
founds  a  system 
of  chemistry  on 
the  theory  of 
phlogiston,  p. 
135. 


1695.  Woodward, 
on  fossils  and 
succession  of 
formations  in 
England,  p. 
216. 


1674.  Malpighi 
on  structure  of 
plants,  p.  140. 

1677.  Leeuwen- 
hoeck  discovers 
animalcules,  p. 
139- 

1682,  Grew  on 
structure  of 
plants,  p.  140. 


1690.  Rivi  nus 
proposes  to  give 
two  names  t  o 
each  plant,  p. 
209. 

1693.  Ray  and 
Willughby's 
classification  of 
animals ;  Ray's 
system  of  plants, 
pp.  142-146. 

1694.  Tourne- 
fort's  system  of 
plants,  p.  145. 


1707.  Buffonand 
Linnseus  bom, 
p.  204. 


1727.  Hales  on 
respiration  of 
plants  and  for- 
mation of  sap, 
P-  193- 


446 


CHRONOLOGICAL    TABLE. 


PROGRESS    OF   MODERN    SCIENCE. 

FROM    A.D.     1738    TO     1 766. 


Astronomy. 

Physics  and 
Mechanics. 

Chemistry. 

Physical 

Geography  and 

Geology. 

Biology. 

1738.        Bougier 

makes  the  first 

1740.  Hawksbee's 

1740.         Lazzaro 

attempt  to  mea- 

electrical     ma- 

Moro _  on     the 

1741.      Linnaeus' 

sure  the  earth's 

chine,  p.  123. 

formation  of  the 

botanical     gar- 

density, p.  278. 

1744.     Celsius, 
Fahrenheit,  and 
Reaumur  mark 

crust      of     the 
earth,  p.  216. 

den  at  Upsala, 
p.  208. 
1743.      Haller  on 
contraction     of 
the      muscles  ; 
anatomical 

off  degrees    on 

plates,  pp.  195- 

thermometer,  p. 

.197. 

120. 

. 

1746.     Franklin's 

» 

1 

experiments    in 

1748.    Haller  and 

electricity,      p. 

Hunter  on  com- 

254- 

parative      ana- 

tomy, p.  197. 

1749.   Hutton  be- 

1749.   Buffon's 

gins  to  examine 

'  Natural    His- 

the   formations 

tory  ; '  distribu- 

of   the    earth's 

tion  of  animals. 

crust,  p.  219. 

p.  205. 
1750.       Dauben- 
ton's    anatomy. 

1752.        Franklin 

p.  205. 

proves  identity 

1753.    Linnseus 

of       electricity 

introduces  spe- 

and   lightning. 

cific  names,  p. 

p.  256. 

1756.      Black  ex- 

208. 
1754.    Bonnet  on 
leaves  of  plants, 

1757.      Dollond's 

tracts       *  fixed 

p.  200. 

achromatic  tele- 

air' from  lime- 

scope, p.  169. 

stone    and    ex- 

1760.    Black   on 

amines  it,  p.  226. 

1 761.     Sun's  dis- 

latent   heat    in 

1761.     Bergmann 

tance  first  mea- 

melting ice  and 

on  chemical  af- 

1762. Bonnet  and 

sured    by    the 

in  steam,  p.  241. 

finity  & ' tests : ' 

Spallanzani   on 

transit    of    Ve- 

proves that 

regrowth  of  se- 

nus ;     Delisle's 

fixed  air  is  an 

vered  limbs,  p. 

method     intro- 

acid, p.  228. 

201. 

duced,  pp.    162 

and  266. 

1764.    Bonnet  on 

1 764- 1 780.       La- 

development of 

grange,      libra- 

1765.      Watt's 

animals,  p.  202. 

tionofthemoon. 

steam  -  engine. 

1766.    Cavendish 

p.  267. 

pp.  244-249. 

discovers      hy- 

drogen, p.  230. 

CHRONOLOGICAL   TABLE. 


447 


PROGRESS   OF   MODERN   SCIENCE. 

FROM    A.D.     1769    TO    1 7  89. 


Astronomy. 


1774.  Maskelyne 
measures  the 
earth's  density 
by  Schehallien 
experiment,  p. 
277. 

1774-1783.  La- 
place on  long 
inequality  o  f 
Jupiter  and  Sa- 
turn ;  moon's 
acceleration,  p. 
269. 

1776.  Lagrange 
proves  the  sta- 
bility of  the 
planetary  or- 
bits, p.  270. 


1781.  Uranus 
discovered  by 
Herschel,  p.  272. 

1783.  Proves  the 
rotation  of  bi- 
nary stars,  p. 
273- 


1786.  He  dis- 
covers star-clus- 
ters and  nebu- 
lae, p.  274 ;  and 
the  motion  of 
the  solar  sys- 
tem towards 
Hercules,  p. 
275- 


Physics  and 
Mechanics. 


1769.  Boulton 
and  Watt  part- 
ners, p.  251. 


1785.  Watt's 
double  -  acting 
steam  -  engine, 
p.  251. 


1789.  Electricity 
experiments  of 
Galvani ;  con- 
troversy between 
Volta  and  Gal- 
vani, pp.  259- 
261. 


Chemistry. 


1772.  Rutherford 
describes  nitro- 
gen, p.  23s. 

1774.  Priestley 
discovers  oxy- 
gen, p.  231. 


1775.  Scheele  dis- 
covers oxygen, 
p.  231. 


1778.  Lavoisier 
overthrows  the 
theory  of  'phlo- 
giston '  by  prov- 
ing the  action 
of    oxygen,    p. 

235- 

1779.  Shows  the 
composition  of 
carbonic  acid, 
p.  238. 

1784.  Cavendish 
explodes  oxy- 
gen and  hydro- 
gen, forming 
water,  p.  231. 

1787.  Lavoisier 
founds  a  new 
chemical  no- 
menclature,   p. 

239. 
1789.    Lavoisier's 
*  Elements      of 
Chemistry'  pub- 
lished, p.  239. 


Physical 

Geography  and 

Geology. 


1769.  Cook's 
voyage  to  the 
South  Seas  for 
the  second  tran- 
sit measure- 
ment, p.  162. 


1775.  Werner  lec- 
tures on  geo- 
logy at  Frey- 
berg,  p.  217. 


1784.  Disputes 
between  Nep- 
tunists  and  Vul- 
canists,  p.  218. 

1785.  Sir  James 
Hall  on  melted 
rock  ;  Hutton 
on  granite  veins, 
p.  221. 

1788.  Button's 
'  Theory  of  the 
Earth'  publish- 
ed, p.  219. 


Biology. 


1768.  Foundation 
of  the  Linnaean 
system  ;  *  Sys- 
tema  Naturae ' 
completed,  pp. 
210-211. 

1772,  Priestley  on 
breathing  of 
plants,  p.  232. 


1778.  Death  of 
Linnaeus  ;  his 
collections 
brought  to  Eng- 
land, p.  212. 


1783.  Hunter's 
museum  begun 
in  Leicester 
Square,  p.  199. 


1789.  Animal  elec- 
tricity disco- 
vered by  Gal- 
vani, p.  259. 

1789.  Jussleu 

founds  the  Na- 
tural System  of 
plants,  p.  382. 


448 


CHRONOLOGICAL   TABLE. 


PROGRESS   OF   MODERN   SCIENCE. 

FROM  A.D.    1790  TO    181I. 


Astronomy. 


1793.  Herschel 
on  cause  of  sun- 
spots,  p.  353. 


1799.  Laplace's 
'Mecaniqu  e 
Celeste,'  p.  271. 


:8oi.  Piazzi  dis- 
covers Ceres, 
the  first  of  the 
asteroids,  p.  289. 


1802-4-7.  Dis- 
covery of  other 
asteroids.  Ol- 
bers  suggests 
they  are  frag- 
ments of  a 
planet,  p.  290. 

1803.  Biot  on  me- 
teoric stones,  p. 
297. 


Physics  and 
Mechanics. 


1792.  Voltaic  or 
chemical  elec- 
tricity, p.  261. 

1798.  Rumford 
boils  water  by 
friction,  p.  330. 

1799.  Davy  melts 
ice  by  friction, 

P-  333- 

1800.  Voltaic 
pile,  p.  263. 

1800.  Sir  W.  Her- 
schel discovers 
dark  heat-rays, 
P-  315- 


1801.  Ritter  dis- 
covers chemical 
rays,  p.  316. 

1 801.  Young  on 
interference  of 
light,  p.  302. 

1802.  Wedgwood 
and  Davy,  sun- 
pictures,  p.  317. 

1802.  Wollaston 
lines  of  spec- 
trum, p.  318. 


1804.  Fraunhofer 
compares  lines 
in  the  spectrum 
of  sun  and  stars, 
p.  319- 


1808.  Malus  dis- 
covers polarisa- 
tion of  light  by 
reflection,  p. 
309- 

181 1.  Leslie  and 
Melloni  on  heat 
rays,  p.  340. 


Chemistry. 


1794.  Lavoisier 
guillotined,  p. 
240. 


1800.  Nicholson 
and  Carlisle,  de- 
composition of 
water,  p.  364. 

1800.  Davy  on 
laughing  gas, 
P-  363- 


1806.  Davy  on 
electrolysis  ; 
discovers  potas- 
sium and  so- 
dium, p.  364. 

1807.  Davy  on 
hydrochloric 
acid,  p.  365. 

1808.  Dal  ton, 
law  of  multiple 
proper  tions  ; 
atomic    theory, 

PP-  371-374- 
1808.      Gay-Lus- 
sac  on  combina- 
tion in  multiple 
volumes,  p.  377. 


Physical 

Geography  and 

Geology. 


1790.  Wm.  Smith 
studies  the  suc- 
cession of  strata, 
p.  222. 

1790.  De  Saus- 
sure  studies  the 
action  of  gla- 
ciers, p.  412. 


1799.  Humboldt's 
journeys  in 
America.  He 
traces  isother- 
mal lines,  p. 
385. 


Biology. 


1790.  Goethe  on 
the  metamor- 
phosis of  plants, 
p.  381. 


1800.  Cuvier's 
lectures  on  ana- 
tomy ;  he  in- 
sists on  the  fit- 
ness of  organisa- 
tion in  indi- 
vidual animals, 

P-  395- 

1 801.  Lamarck 
on  development 
of  animals,  p. 
391- 


1802.  G.  St.-Hi- 
laire  brings  zoo- 
logical collec- 
tions    from 

Egypt,  p-  391- 


804.  Humboldt 
on  distribution 
o(  p'ants,  p.  385. 


CHRONOLOGICAL   TABLE. 


449 


RISE    OF    MODERN    SCIENCE. 

FROM  A.D.    l8l2  TO    1 848. 


Astronomy. 

Physics  and 
Mechanics. 

Chemistry. 

Physical 

Geography  and 

Geology. 

Biology. 

1812.     Former 

1812.    Cuvier  re- 

periods   of   life 

stores  the  fossil 

on    the     globe 

animals  of  Paris, 

proved      by 

p.  397- 

Cuvier,  p.  397. 

1815.      Davy's 

1815.  W.  Smith's 

safety-lamp,   p. 

geological  map. 

363. 

p.  224. 

1 816.        Fresnel 

and  Young,  po- 

1817.   Buckland's 

1817.         Cuvier 's 

larization        of 

geological    lec- 

'Animal King- 

light, p.  311. 

1818.      Berzellius 

tures,  p.  405. 

dom  '  published, 
p.  396. 
1818.    G.  St.-Hi- 

1819.     Encke's 

1819.        Oersted, 

on  use    of   the 

laire  on  unity  of 

comet,  p.  2qo. 

electro-magnet- 

blow -  pipe,    p. 

plan  in  animals. 

ism,  p.  342. 

370. 

P-  393- 

1S20-1838.    SirJ. 

1820.        Ampere, 

Herschel  studies 

electro-magnet- 

stars     of     the 

ism,  p.  345. 

southern  hemi- 

1821.      Faraday, 

sphere  ;  Magel- 

electro-magnet- 

lanic clouds,  p. 

ism,  p.  349. 

295- 

1822.   Seebeck  on 
thermo  -  electri- 

1822.      Herschel 
on  use  of  spec- 

city, p.  352. 

troscope  to  de- 

1825.     McEnery 

1826-60.  Schwabe 

1826.       Mo  bill 

tect      chemical 

discovers     flint 

proves  periodi- 

proves     the 

elements,  p.  321. 

tools,  with  bones 

1828.    Von  Baer's 

city      of     sun- 

truth  of  animal 

of   extinct  ani- 

law of  embryo- 

spots,  p.  353. 

electricity,      p. 

mals  in  Kent's 

logical  develop- 

1826.     Biela's 

261. 

Cavern,  p.  416. 

ment,  p.  400.       1 

comet,  p.  2gi. 

1830.        Liebig's 
analyses  of  or- 
g  a  n  i  c      s  u  b- 
stances,  p.  377, 

1830.  Lyell's' Geo- 
logy ; '    he    in- 
sists    on    suffi- 
ciency of  causes 

1 
1 

1832.     Discovery 

like  the  present 

1832.      Death   of 

s 

of      chloroform 

to    explain  the 

Cuvier,  p.  400. 

and  chlorale  by 

past  history  of 

Liebig,  p.  378. 

the     globe,    p. 

1834.  Faraday  on 

405- 

1837.  WheatsLone 

electrolysis; 

1838.     Herschel's 

and  Cooke,  elec- 

chemical nature 

1840.    Agassiz  on 

'  Outlines  of  As- 

tric   telegraph. 

of  electric  cur- 

glacial    period 

1839.    Agassiz 

tronomy  '    pub- 

P- 356. 

rent;  invention 

and  blocks  car- 

on     freshwater 

lished,  p.  2q6. 

1839-42.     Seguin 

of     voltameter. 

ried    over    Eu- 

fishes, p.  410. 

and   Mayer  on 

P-  367- 

rope  by  ice,  p. 

1840-48.  Organic 

relation  between 

411. 

chemistry,      p. 

heat  and  work. 

377. 

P-  335- 

1839.  Daguerreo- 

types, p.  317. 

450 


CFIRONOLOGICAL    TABLE, 


RISE    OF    MODERN    SCIENCE. 

FROM    A.D.     1843    TO    1 874. 


Astronomy. 


1845.  Division  of 
Biela's  comet, 
p.  290. 

1845-6.  Adams 
and  Leverrier 
work  out  the 
position  of  Nep- 
tune ;  Galle  finds 
the  planet,  p. 
290. 

850.  Lamont, 
periodicity  of 
magnetic  dis- 
turbance, p.  355. 


859.  Carrlngton 
and  Hodgson, 
sun  -  spot  and 
magnetic  dis- 
turbance, p.  355. 


1862-66.  Schiape- 
relli,  Adams, 
and  Leverrier, 
discover  the  or- 
bits of  comets 
and  meteor  sys- 
tems, p.  298. 

1874.  Expeditions 
to  observe  the 
transit  of  Venus, 
p.  162. 


Physics  and 
Mechanics. 


1843-49.  Joule 
on  equivalent 
of  heat ;  dyna- 
mical theory  of 
heat,  p.  335. 
-  Hirn's  experi- 
ments on  heat, 
P-  338. 


:  860-1 866.  Four 
nev/  metals  dis- 
covered by  spec- 
trum analysis, 
P-  323- 


1861.  Bunsenand 
Kirchhoff  dis- 
cover the  mean- 
ing of  the  lines 
in  the  spectrum, 

P-  323- 

1862.  Huggms 
and  Miller, 
spectrum  analy- 
sis of  the  stars 
and  nebulae,  p. 
326. 

—  Alexander 
Herschel,  spec- 
trum of  falling 
stars,  p.  328. 


Chemistry. 


548.  Wohler 
makes  organic 
elements  artifi- 
cially, p.  397. 
56i.  Metals  in 
the  atmosphere 
of  the  sun  and 
stars  discovered 
by  spectrum 
analysis,  p.  326. 
1862.  Gas^  of 
the  nebulae  dis- 
covered by  spec- 
trum analysis, 
P-  327- 


Physical 

Geography  and 

Geology. 


1847.  Boucher  de 
Perthes  dis- 
covers flint  im- 
plements  at 
Abbeville,  p. 
415- 


1853.  Discovery 
of  Swiss  lake- 
dwellings,  p. 
416. 

1858.  Humboldt's 
*  Cosmos '  pub- 
lished ;  death  of 
Humboldt,  p. 
386. 


1863.  ^  Lyell's 
•  Antiquity  of 
Man,'  p.  418. 


Biology. 


1858.  Theory  of; 
natural      selec- 
tion by  Darwin 
and      Wallace, 
p.  426. 

1859.  Darwin  s 
'  Origin  of  Spe- 
cies,' p.  425. 


1852-1872.  Dis- 
covery of  inter- 
mediate fossil 
forms,  p.  424. 


bO 

Hippocrates ;     Aristotle  ; 
Theophrastus  ;    Erasis- 
tratus ;    Herophilus  ; 
Galen. 

1 
1 

1 
i 

Vesalius  ;  Fallopius ;  Eu- 
stachius  ;  Gesner  ;  Cai- 
salpinus ;  Fabrlcius. 

Harvey;  Asellius ;  Riid- 
beck  ;  Malpighi :  Leeu- 
wenhoeck  ;  Grew  ;  Ray  ; 
Willughby ;  Toumefort. 

Boerhaave;  Hales;  Hal- 
ler ;    Hunter ;  Bonnet ; 
Spallanzani ;  Buffon  ; 
Daubenton  ;  Linnsus : 
Jussieu. 

Lamarck  ;  Goethe  ;  G.  St.- 
Hilaire  ;  Cuvier  ;  Von 
Baer  ;    Boucher  de 
Perthes ;  Darwin  ;  Wal- 
lace ;  Agassiz. 

-a 

3 

§*  • 

Wo 
'!n 

Anaximander. 

Pythagoras. 

Eratosthenes. 

Ptolemy. 

Strabo. 

Avicenna. 
Columbus. 
Vasco  di  Gama. 
Magellan. 

Ofin 

Steno. 
Scilla. 
Woodward. 

Lazzaro  Moro. 
Werner. 
Hutton. 
William  Smith. 
De  Saussure. 

Humboldt. 

Buckland. 

Lyell._ 

Agassiz. 

Murchiscn. 

1/1 

's 

o 

Marcus  Grsecus. 
Geber. 
Roger  Bacon. 

a 

Mayow. 
Beecher. 
Stahl. 

Boerhaave  ;   Hales  ; 
Black  ;    Bergmann ; 
Cavendish ;    Priestley ; 
Scheele  ;    Rutherford  ; 
Lavoisier. 

Wollaston  ;  Berzelius ; 
Biot ;    Dalton ;   Thom- 
son ;   Gay-Lussac  ; 
Davy ;    Faraday ;    Lie 
big  ;  Wohler  ;  Bunsen  ; 
Miller. 

o 

V 

H-5 

Gerbert ;    Ben  Musa  ; 
Alhazen ;  Roger  Bacon ; 
Vitellio  ;  Flavio  Gioja  ; 
Leonardo  da  Vinci. 

(U 

Snellius ;    Descartes  ; 
Bacon  ;  Drebbel ;  Tor- 
ricelli ;  Guericke ; 
Boyle ;   Hooke  ;   Huy- 
ghens ;  Roemer. 

Du  Faye  ;  Celsius  ; 
Fahrenheit ;  Reaumur ; 
Watt ;  Franklin  ;  Gal- 
vani ;  Volta  ;  Rumford. 

Young ;  Malus  ;  Fresnel ; 
Arago  ;   Oersted  ;   Am- 
pere ;  Seebeck ;   Brew- 
ster ;   Sabine  ;    Fraun- 
hofer  ;  Kirchhoff ;  Hug- 
gins  ;  Mayer ;  Joule  ; 
Wheatstone. 

6 
o 

a 

e 

Thales,   Anaximander; 
Pythagoras ;  Anaxa- 
goras  ;    Democritus  ; 
Eudoxus  ;  Aristotle  ; 
Aristarchus ;  Hippar- 
chus ;  Ptolemy. 

u5 

■3.2 

Copernicus. 
Tycho  Brahe. 
Giordano  Bruno. 

Galileo  ;  Kepler ;  Gas- 
sendi ;  Horrocks ; 
Newton ;  Huyghens  ; 
Halley. 

Bradley ;  Delisle  ; 
Lagrange ;  Laplace  ; 
Herschel ;  Maskelyne. 

Piazzi ;   Olbers  ;   Encke  ; 
Gauss ;  Sir  J.  Herschel ; 
Airy  ;  Adams ;    Lever- 
rier  ;  Galle  ;  Schwabe  ; 
Sohiaparelli. 

1 

Middle 
Ages. 

Sixtheenth 
Century. 

lb 
a  3 

4)0 

S  3 

«  2 
■S  c 

p 


INDEX. 


ABBEVILLE 

ABBEVILLE  flint  implements,  415 
Aberration  of  fixed  stars,  265 
Academies  of  science  founded,  124 
'  Academy  of  Secrets '  at  Naples,  74 
Achromatic  telescopes,  169 
Acids,  strong,  discovered  by  Geber,  45 
Adams  calculates  the  position  of  Neptune, 

292  ;  on  November  meteors,  299 
^sculapius  god  of  medicine,  15 
Aerial  acid,  Bergmann  on,  230 
Agassiz,  his  history,  410  ;  on  glacial  period, 

411-15  ;    his  natural  history  school,  411  ; 

recognises  glaciation  in  Scotland,  414 
Aigle,  meteoric  stone-fall  at,  297 
Air,    Boyle  and   Hooka,    experiment   on, 

130  ;  Mayow  on,   131 ;  -cells  studied  by 

Malpighi,   138 ;  -pUmp,  section  of,  121  ; 

Guericke's,  121 ;  -tubes  of  insects,  139 
Airy,  Adam's  paper  on  Neptune  sent  to,  293 
Albategnius  calculates  length  of  year,  45 
Albinus,  anatomical  drawings  of,  196 
Alchemists,  Arabian,  41 
Aldebaran,  spectrum  of,  327 
Alembert,  d',  brings  Laplace  to  Paris,  267 
Alexandria,  founding  of  the   city  of,   18  ; 

school  of  learning  at,  18  ;  taken  by  the 

Arabs,  39 ;  Egyptian  animals  preserved 

at,  391 
Algebra,  an  Arabian  name,  46 
Alhazen  on   eyesight,   47  ;    on  refraction, 

47 ;  on  atmospheric  refraction,    48  ;   on 

magnifying  power  of  lenses,  49 
Alps,  glaciers  of  the,  412 
Amazons,  closely  related  butterflies  of  the, 

420 
Amber,  electric  nature  of,  77 
America,  Agassiz  natural  history  school  in, 

411  ;  glaciation  of,  414 
Ammonia,  origin  of  name,  45 
Ampere,  early  life  of,  343 ;  on  direction  of 

magnetic  current,  345  ;   on  electro-mag- 


ANIMALS 

nets,  347  ;  invents  the  galvanometer,  351  ; 
on  cause  of  terrestrial  magnetism,  352 ; 
suggests  electric  telegraph,  357 

Analysis  term  explained,  371 ;  of  sub- 
stances by  tests,  229  ;  of  organic  sub- 
stances, 192,  377  ;  different  methods  of, 
369 ;  Spectrum-,  315 

Anatomy,  Erasistratus  and  Herophilus  on, 
26 ;  Vesalius  on,  67 ;  Eustachius  and 
Fallopius  on,  68  ;  vegetable-,  140  ;  rise  of 
comparative,  197 ;  Haller  and  Hunter 
on,  199  ;  Cuvier  on,  395 

Anatomical  plates  of  Vesalius,  67  ;  of  Haller, 
196 

Anaxagoras  on  the  moon  and  on  eclipses, 
13 ;  banished,  14 

Anaximander,  science  of,  9 

Anderson  brings  Newcomen  engine  to  Watt, 

245 

Anderson,  Mr.,  gave  Penikese  island,  411 

Animal,  substances  made  of  altered  vege- 
table matter,  194 ;  electricity,  259,  261 

Animalcules,  discovery  of,  140 

Animals,  Cuvier  on  internal  structure  of, 
396 ;  fossil,  restored  by  Cuvier,  397  ; 
Lamarck  on  development  of,  393 ;  simi- 
larity of  structure  in,  394 ;  difficulty  in 
distinguishing  species  of,  420 ;  useless 
organs  in,  421  alike  in  the  embryo,  421  ; 
living  and  fossil  nearly  related,  422  ; 
gradual  succession  of,  on  the  globe,  422- 
424  ;  selection  of  by  man,  428  ;  natural 
selection  of,  427,  429  ;  fossil,  intermediate 
forms  of,  424 

Animals  and  plants,  Aristotle  on  links 
between,  16 ;  history  of,  by  Gesner, 
69  ;  classified  by  Ray  and  Willughby, 
142  ;  Linnaeus  gives  specific  names  to, 
210;  Buffon  on  distribution  of,  205  ; 
Grew  and  Malpighi  on,  137-142 ;  Dar- 
win and  Wallace  on,  426 


454 


INDEX. 


ANTIQUITY 

Antiquity  of  man,  415  ;  Lyell's  work  on, 
418 

Aphides,  Bonnet  on,  200 

Apollo,  god  of  the  sun,  8 

Apple,  Newton  and  the,  149  ;  -leaf,  skin  of, 
showing  stomates,  141 

Aqueous  rocks,  Hutton  on,  220 

Arabs,  conquests  of  the,  39  ;  bum  Alex- 
andrian library,  39  ;  science  of  the,  40  ; 
chemistry  of  the,  41 ;  gunpowder  known 
to  the,  42  ;  medical  schools  of  the,  40 

Arago  on  polarisation  of  light,  311 ;  on 
electro-magnetism,  347  ;  on  Biela's  comet, 
291 

Archimedes  on  the  lever,  22 ;  on  Hiero's 
crown  and  specific  gravity,  23  ;  screw  of, 
25  ;  killed  in  the  Punic  war,  25 

Areas  described  by  planets  about  their 
centre,  100 

Aristarchus  taught  that  the  earth  moves 
round  the  sun,  20  ;  discovered  obliquity 
of  ecliptic,  21 ;  and  rotation  of  the  earth 
on  its  axis,  21 

Aristotelians,  dogmatism  of  the,  81,  106 

Aristotle  on  astronomy  and  zoology,  16 ; 
on  development  of  animals,  419 

Arteries,  passage  of  blood  in,  11 1 ;  throb- 
bing of  explained,  112 

Articulata,  term  explained,  396 

Asellius  on  lacteals  and  nourishing  fluid, 
ii4_ 

Astatic  needle  of  the  telegraph,  359 

Asteroids,  or  minor  planets,  289 

Astrology  of  the  Arabs,  45 

Astronomy,  definition  of,  2  ;  of  Thales,  8  ; 
of  Anaximander,  9;  of  Anaxagoras,  13  ; 
of  Aristotle,  15  ;,of  Aristarchus,  20;  of 
Hipparchus,  29 ;  of  Ptolemy,  32 ;  of 
Albategnius,  45  ;  of  Ebn  Junis,  46 ;  of 
seventeenth  century,  182-184  ;  of  eigh- 
teenth century,  284  ;  of  nineteenth  cen- 
tury, 288 

Atmosphere,  refraction  of  sun's  rays  in 
the,  48 ;  varying  weight  of  the,  118  ; 
pressure  of  the,  122 

Atomic  theory,  374 ;  difficulties  of  the,  376 

Atoms,  definition  of  term,  375 ;  weight  of 
chemical,  374  ;  of  all  the  planets  attract 
each  other,  151 

Attraction,  by  electricity,  77,  123  ;  of 
gravitation  decreases  with  square  of  the 
distance,  152 

Aurora  borealis  coincident  with  outbreak 
of  a  sun-spot,  356 

Australia,  fossil  and  living  pouched  animals 
of  422 


BONNET 

Authority  valued  more  than  truth  in  the 

Dark  Ages,  105 
Avicenna  on  minerals,  50 


BACON,  Roger,  his  'Opus  Majus,'  52 
Bacon,    Francis,    his    influence    on 

science,  103  ;  on  heat,  330 
Bagdad,  medical  school  of,  40 
Bain's  telegraph,  361 
Balloons,  hydrogen  used  for  filling,  231 
Barometer,  invention  of  the,  1 16-19 
Bartholinus  on  double  refraction  in  Iceland 

spar,  180 
Basalt,  disputes  about  formation  of,  219-31 
Bates  on  species  of  Amazon  insects,  420 
Battery,  first  electric,  262 
Becher  proposes  theory  of  Phlogiston,  135 
Beddoes,  Dr.,  employs  Davy,  363 
Beehive,  star-cluster  called  the,  275 
Bees,  clover  fertilised  by,  429 
Ben  Musa,  Arabian  mathematician,  46 
Bergmann  on  chemical  affinity,    228  ;  on 

tests  of  mineral  waters,  229  ;  on  '  fixed 

air,'  230  * 

Berzellius — His  discoveries  by  electrolysis, 

367  ;  on  use  of  blowpipe,  367 
Betelgeux,  no  hydrogen  in  light  of,  327 
Bichat  cited,  380 
Biela's    comet    alarmed    the    world,    291  ; 

divided  into  two,  292 
Binary  stars,  Herschel  discovers,  273 
Biology,    definition  of,  2  ;  of  seventeenth 

century,    T85  ;   spread  of    in  eighteenth 

century,  190 
Blot  on  meteoric  stone-fall,  298  ;  on  polari- 
sation, 314 
Birds,  Ray  and  Willughby  on,  144  ;  rapid 

multiplication  of,  429 
Black  discovers  '  fixed  air,'  226-228  ;   on 

latent    heat,    241-243  ;    Young    studies 

under,  303 
Blood,  circulation  of  the,   iJi-13;  earlier 

theories  about,   no;   air-bubbles  drawn 

out  of  the,  134 
Blowpipe,  Berzellius  on  use  of,  367 
Blumenbach  cited,  380 
Bode's  law,  289 
Boerhaave,    his  character  and    influence, 

191  ;    on    organic    chemistry,    192 ;    on 

juices  of  plants,  193  ;  on  fluids  of  animals, 

194  ;  his  death,  194 
Bonnet's    experiments     on     aphides    and 

plants,    200 ;     on    regrowth    of  severed 

limbs,  201  ;  on  development  of  animals, 


INDEX. 


455 


BOTANICAL 

Botanical  garden  of  Gesner,  6g 

Botanist,  Theophrastus  the  first,  17 

Botany,  different  kinds  of,  2 ;  writers  on, 
17,  70,  IT-,  142,  206,  381,  38s,  389 

Boucher  de  Perthes  finds  ancient  flint  im- 
plements, 415 

Bougier  measures  the  density  of  the  earth, 
278 

Boulton,  partner  of  Watt,  251 

Boyle  one  of  the  founders  of  Royal  Society, 
125  ;  his  air-pump,  124  ;  his  law  of  com- 
pressibility of  gases,  128 ;  his  experi- 
ments on  air,  130 

Bradley  on  aberration  and  nutation,  265 

Brain  described  by  Erasistratus,  26 

Breathing,  Mayow  on,  132 

Brewster,  Sir  D.,  on  polarisation,  314 ;  on 
spectrum  analysis,  321-23 

British  Museum,  meteoric  stones  in  the, 
297 

Bronze  tools  of  lake-dwellings,  417 

Brougham,  Lord,  his  article  against  Young, 

311 

Bruno  burnt  at  the  stake,  83 

Buckland,  his  Cambridge  lectures,  405  ;  on 
glaciation  of  Wales,  414 

BufFon,  history  of,  204  ;  his  work  on  na- 
tural history,  205 ;  and  Linnaeus  com- 
pared, 207  ;  patronises  Lamarck,  389 

Bunsen  on  dark  lines  in  solar  spectrum, 
323 


C^SALPINUS  on  plants,  71  ;  on  cir- 
culation of  the  blood,  in 

Caesium  discovered,  323 

Cairo,  medical  school  of,  40 

Caloric,  old  term  for  heat,  330 

Camera  obscura,  invention  of  the,  75 

Camper  cited,  380 

CandoUe,  Auguste  de,  on  metamorphosis 
of  plants,  384 

Capillaries  discovered  by  Malpighl,  138 

Carbonic  acid  obtained  by  Black,  226 ; 
tested  by  Bergmann,  230 ;  its  nature 
discovered  by  Lavoisier,  238 

Carlisle  on  decomposition  of  water  by 
electricity,  364 

Carnot  on  heat  converted  into  motion,  338 

Carrington,  Mr.,  on  outbreak  of  a  sun- 
spot,  355 

Cassini  on  velocity  of  light,  173 

Catastrophists  in  geologj',  405 

Cats,  their  indirect  influence  on  growth  of 
clover,  429 

Caus'  engine,  246 


COLUMBUS 

Cavendish  discovers  hydrogen,  230 ;  on 
composition  of  water,  231 ;  his  experi- 
ment on  weight  of  the  earth,  279 

Caxton  the  printer,  55 

Cellular  tissue,  section  of,  140 

Celsius  invents  centigrade  scale,  12c 

Centigrade  scale,  120 

Ceres  discovered  by  Piazzi,  289 

Charles  I.,  riots  in  reign  of,  124  ;  IL 
grants  Royal  Society  charter,  125  ;  V. 
of  Spain  protects  Vesalius,  68 

Chemical,  rays  discovered,  315  ;  rays  of 
action  in  photography,  317  ;  nomencla- 
ture of  Lavoisier,  239  ;  elements,  weight 
of,  373  ;  symbols,  376 ;  or  Voltaic  elec- 
tricity, 261  ;  theory  of  electricity,  367 

Chemical  affinity,  Bergmann  on,  228 : 
Newton  on,  229  ;  power  of  electric  cur- 
rent to  overcome,  367 

Chemistry,  definition  of,  2  ;  of  the  Araos, 
41 ;  of  Geber,  43  ;  of  Paracelsus  and 
Van  Helmont,  72  ;  of  Boyle  and  Hooke, 
130 ;  of  Mayow,  131 ;  Boerhaave  on  01- 
ganic,  194  ;  of  Black,  226  ;  of  Bergmann, 
228  ;  of  Cavendish,  230 ;  of  Priestley , 
231  ;  birth  of  modern,  235  ;  Newton's 
work  on,  destroyed,  170 ;  methods  of 
studying,  369 

Chick,  Harvey  on  development  of,  114 

Chinese,  early  science  of,  4 ;  mariner's 
compass  known  to  the,  54 

Chlorale,  discovery  of,  378 

Chloroform,  "Ciscovery  of,  378 

Cinnamon  tree,  essences  obtained  from,  193 

Cipher,  word  derived  from  Arabic,  46 

Circulation  of  the  blood,  diagram  of,  113 

Circular  polarisation  in  quartz  crystals,  314 

Circumference  of  earth  measured  by  Era- 
tosthenes, 28 

Classifications  of  plants,  70-71,  142,  209, 
382  ;  of  animals,  69,  143,  210,  396 

Clausen  calculates  the  period  of  Biela's 
comet,  291 

Clifford,  Mr.,  befriends  Linnaeus,  207 

Climate,  Humboldt  on  causes  of,  385  ; 
Lamarck  on  effects  of,  393 

Cod-fish,  animalcules  in  roe  of,  140 

College  of  Surgeons,  Hunter's  collection 
in,-  200 

Colours,  prismatic,  167  ;  cause  of  in  tele- 
scopes, 169  ;  caused  by  interference  of 
light,  307  ;  on  the  soap  bubble,  307  ; 
depend  on  light-vibrations,  177 

Columbus,  Christopher,  his  voyages,  56 ; 
discovers  variation  of  magnetic  needle, 
57 


456 


INDEX. 


COLUMBUS 

Columbus  on  circulation  of  the  blood,  1 1 1 

Combustion,  Hooke  on,  130  ;  Mayow  on, 
132 ;  Stahl's  mistaken  theory  of,  135 ; 
cause  of  proved  by  Lavoisier,  238 

Comet,  Halley  predicts  return  of,  163 

Comets,  Newton  on  orbits  of,  155 ;  re- 
turning, 291  ;  and  meteors,  297 

Commutator  of  the  telegraph,  360 

Comparative  anatomy,  rise  of,  197  ;  Hun- 
ter's collection  illustrating,  199  ;  Haller 
on,  197  ;  Cuvier  on,  395-98 

Compass,  figure  of  first  mariner's,  54 

Compound  flowers,  145 

Concluding  remarks,  433 

Condenser,  Watt's  separate,  248-50 

Conservation  of  energy,  339 

Contraction  of  the  muscles,  197 

Cook's  voyage  to  observe  transit  of  Venus, 
162 

Cooke  patents  electric  telegraph,  357 

Copernican  theory,  65  ;  proofs  of  the  truth 
of,  91 

Copernicus,  life  and  work  of,  65 

Cordova,  medical  school  of,  40 

Corpuscular  theory  of  light,  174,  303 

Correlation  of  the  physical  forces,  435 

*  Cosmos '  of  Humboldt,  386 

Crabtree  sees  transit  of  Venus,  158 

Crookes  discovers  thallium,  323 

Crown  of  cups,  Volta's,  262 

Crown-glass,  dispersion  of  light  in,  169 

Crystals,  double  refraction  in,  180;  r-;is- 
sage  of  light-waves  in,  313  ;  circular 
polarisation  in  quartz,  314 

Currents  from  an  electric  battery,  262 ; 
Humboldt  on  ocean,  385-86 

Cuvier,  history  of,  389-95  ;  his  museum, 
391 ;  on  creation  of  animals,  394 ;  his 
discussion  with  St.-Hilaire,  395-397  5  on 
comparative  anatomy,  395  ;  on  classifica- 
tion and  structure  of  animals,  396  ;  on 
fossil  animals  of  Paris,  397  ;  his  '  Osse- 
mens  Fossiles,'  399  ;  death  of,  400 

Cycloidal  pendulums,  175 


DABURON,  Ampere's  visit  to,  344 
Daguerre  fixes  sun-pictures,  317 

Dal  ton,  life  of,  371 ;  on  law  of  multiple 
proportions,  373  ;  atomic  theory,  374 

Dark  ages,  science  of,  39  et  seq. 

Darwin,  his  history,  425 ;  on  origin  of 
species,  426  ;  his  theory  explained,  427- 
431  ;  on  causes  of  natural  selection,  429 

Daubenton's  anatomical  work,  205 

Dav>^  Sir  H.,  his  history,  362  ;  his  experi- 


EARTHQUAKES 

ments  on  nitrous  oxide,  363  ;  on  electro- 
lysis, 364 ;  discovers  potassium  and 
sodium,  365  ;  his  safety  lamp,  363  ;  on 
organic  chemistry,  378  ;  on  sun-pictures, 
317 ;  Sir  H.  melts  ice  by  friction,  333  ; 
his  kindness  to  Faraday,  348 

De  Dominis  on  the  rainbow,  164 

Delisle's  method  of  measuring  transit  of 
Venus,  266 

Deltas,  growth  of,  12 

Democritus  on  the  Milky  Way,  15 

Denudation,  Hutton  on,  220 

Descartes  on  light,  106,  164  ;  on  the  value 
of  doubt,  105 

Development  of  animals,  Lamarck  on, 
391 ;  Von  Baer  on,  402 

Diagram  showing  how  distances  can  be 
measured  on  the  sun's  face,  159 

Diagrams  of  bent  and  broken  rocks,  217, 
218 

Diameter  of  the  sun,  161 

Diamond,  nature  of,  proved  by  Lavoisier, 
238 

Djafer,  or  Geber,  Arabian  alchemist,  43 

Disecious  plants  explained  by  Caesalpinus, 
72 

Dicotyledons  term  explained,  145 

Differential  calculus,  by  Leibnitz,  148 

Disc,  Newton's  rotating,  168 

Dispersion  of  light  discovered  by  Newton, 
J64  ;  in  different  kinds  of  glass,  169 

Distillation  known  to  Geber,  43,  370 

Distribution  of  animals,  Buffon  on,  206  ;  of 
plants,  Humboldt  on,  385 

Dogmatism  of  the  sixteenth  century,  67, 
81,  83 

Dollinger,  anatomist,  401 

Dollond,  Mr.,  makes  achromatic  telescope, 
169 

Double  refraction,  179,  180 

Doubt,  Descartes  on  the  value  of,  105 

Drebbel  makes  alcohol  thermometer,  120 

Ducts  of  plants,  140 

Du  Faye  on  electricity,  254 

Dynamical  theory  of  heat,  335 


EARL'S  COURT,   Hunter  kept   wild 
animals  at,  199 
Earth  declared  by  Aristotle  to  be  a  globe, 
16 ;     circumference    of    measured,    28 ; 
Picart  measures  the  size  of  the,    150 ; 
Newton  on  shape  of  the,  154 ;   measure- 
ment of  density  of  the,  277 
Earth-light  on  the  moon,  89 
Earthquakes,  Pythagoras  on,   12 ;   Strabo 


¥ 


INDEX. 


457 


EBN 

on  causes  of,  33  ;  changes  of  level  caused 

by,  408 
Ebn  Junis,  Arabian  astronomer,  46 
Eclipses  explained  by  Anaxagoras,  13 
Ecliptic  or  sun's  path,  how  traced  out  by 

the   Greeks,  18 ;  Anaxagoras  discovers 

obliquity  of,  21 
Egyptians,  early  science  of,  4 
Eighteenth  century,   work    of    the,    434 ; 

summary  of  science  of,  280 
Elective  affinities,  Bergmann  on,  229 
Electric  currents  causing    magnetic   cur- 
rents, 346  ;  making  electro-magnets,  347  ; 

power  of  to  conquer  chemical  affinity, 

367  _ 

Electrical  machines,  Guericke's,  123  ; 
Hawksbee's,  123 

Electric  spark  observed  by  Guericke,  124 

Electric  telegraph,  invention  of,  357  ;  des- 
cription and  diagrams  of,  357-60  ;  Bain's 
set  on  fire  by  magnetic  storm,  356 ; 
Morse's  and  Steinheil's,  357 

Electricity,  Gilbert  on,  77,  123  ;  attraction 
and  repulsion  by,  124  ;  Du  Faye  on  dif- 
ferent kinds  of,  254 ;  Franklin  on,  255  ; 
and  lightning,  256  ;  positive  and  nega- 
tive, 256  ;  animal,  259  ;  chemical  or  vol- 
taic, 261 ;  chemical  theory  of,  367  ;  pro- 
duced by  heat,  352 

Electrolysis,  discovery  of,  364 ;  Davy's 
experiments  in,  365  ;  Faraday  on,  367 

Electro-magnetism,  Oersted  discovers,  341 ; 
Ampere  on,  345  ;  Faraday  on,  349 

Electro-magnets  made  by  electric  current, 

347 
*  Electron,'  root  of  word  '  electricity,'  77 
Elements,  sixty-four  known,  370 
Ellipses,  planets  move  in,  99 
Embryology,  Von  Baer's  law  of,  ^00  ;  con- 
firms St.-Hilaire's  view  of  homological 

structure,  401 
Embryos  of  animals  alike  in  structure,  42  r 
Emission  theory  of  light,  174,  303 
Encke's  comet,  290 
Energy,  potential    and  active,    337,    339  ; 

conservation  of,  339,  353 
Engines,  history  of,  245  ;   the  Newcomen, 

246  ;  Watt's  double-acting,  250 
England,  geological  map  of,  by  W.  Smith, 

224 
Epidermis  studied  by  Malpighi,  139 
Equinoxes  observed   by  Thales,  9  ;  Hip- 

parchus  discovers  precession  of,  30 
Erasistratus  on  the  brain,  26 
Erratic  blocks  on  the  Jura,  413  ;  a  proof  of 

former  extension  of  ice,  414 

21 


FRENCH 

Eratosthenes  lays   down  first  parallel    of 

latitude,  27  ;  measures  circumference  of 

the  earth,  28 
Ether,  light  a  vibration  of  the,  176 
Euclid,   some  problems  of,    invented    by 

Thales,  9 
Euclid    discovers     that     light    travels    in 

straight  lines,  21 
Eudoxus     explains     movements     of     the 

planets,  15 
Eustachius  the  anatomist,  68 
Evolution,  theory  of,  435 
Extinct  animals,  restored  by  Cuvier,  398  ; 

man  contemporary  with,  415 
Eye,   Alhazen   on  the  sight   of  the,    47  ; 

Porta  on  structure  of  the,  76  ;  Kepler  on 

the,  96 


FABRICIUS  Aquapendente  discovers 
valves  in  veins,  in 

Fahrenheit  thermometer,  freezing  point  of, 
120 

Falling  bodies,  Galileo  on  rate  of,  80 

Falloplus,  the  anatomist,  68 

Faraday,  history  of,  348  ;  on  rotation  of 
magnets  and  electric  wires,  349 ;  on 
electric  current  produced  by  a  magnet, 
351  ;  on  connection  between  electricity 
and  chemical  changes,  367 

Faust,  John,  the  printer,  55 

Fire-air  discovered  by  Mayow,  132  ;  its 
effect  on  the  blood,  134 

'  Fixed  air,'  Black  on,  226-228 ;  Berg- 
mann tests,  230 

Flame  consuming  'fire-air,'  132;  spectra 
of  different  kinds  of,  321 

Flint  implements  of  Abbeville,  415 

Flint-glass,  dispersion  of  light  in,  169 

Flood,  attempt  to  explain  fossils  by  a 
universal,  215 

Flowers,  plants  classified  by  their,  145 

Fluxions,  Newton's  method  of,  148,  153 

Force,  convertibility  of,  369 ;  of  gravita- 
tion, 149 

Fossil  animals  restored  by  Cuvier,  327  ; 
intermediate  forms  of,  424 

Fossil  shells  observed  by  Pythagoras,  11 

Fossils,  Gesner  on,  7<3*;  first  attempts  to 
explain,  215 ;  used  by  W.  Smith  for 
classification,  223 

Franklin's  early  life,  253  ;  his  experiments 
in  electricity,  255  ;  he  proves  lightning 
to  be  electricity,  256-258 

Fraunhofer's  early  life,  319  ;  lines,  320 

French  school  of  chemistry,  239 


45S 


INDEX 


FRESNEL 

Fresnel,   history  of,  311 :    on  polarisation 
of  light,  311;    on  circular  polarisation, 

314 

Freyberg,  Werner's  lectures  at,  217 

Friction,  ice  melted  and  water  boiled  by, 

333 
Friendship  of  Ray  and  Willughby,  143 
Frog's  leg,  electricity  in,  259-61 


GALEN,  physiology  of,  34  ;  corrected 
by  Vesalius,  67 
Galileo  on  the  pendulum,  79  ;  on  falling 
bodies,  80 ;  on  motion  of  heavy  bodies,  82  ; 
on  secondary  light  of  the  moon,  89 ;   on 
Jupiter's  moons,  91  ;  on  phases  of  Venus, 
91 ;  on  sun-spots  and  rotation   of  sun  on 
its  axis,  91  ;   demonstrates  the  truth  of 
Copernican  theory,  91,  102  ;  his  telescope, 
89  ;    his    recantation,  93  ;    his  blindness 
and  death,   94 ;  on  rising  of  water  in  a 
pump,  116  ;  makes  a  water  thermometer, 
120 ;   compared  with  Tycho  and   Kep- 
ler, 102 
Galle  finds  Neptune,  294 
Galvani    on   animal   electricity,    259 ;    his 
controversy  with  Volta,  260 ;  his  death, 
261 
Galvanism,  260 

Galvanometer  invented  by  Ampere,  351 
Ganges,  mud  carried  down  by  the,  407 
'  Gas,'  term    used  by  Van  Helmont,  73  ; 

Nebulae  composed  of,  275 
Gases,  Boyle's  law  of,  128  ;    Bacon  on,  52  ; 
Mayow  on,  132  ;    discovery  of  the  four 
important,  225  ;   spectra  of,  322 ;   atmo» 
sphere  of,  round  the  sun,  325    , 
Gassendi  observes  transit  of  Mercury,  157 
Gauss  rediscovers  Ceres,  290 
Gay-Lussac  on  multiple  volumes,  377 
Geber  the  founder  of  chemistry,  43-45 
Geist,  word  '  gas '  derived  from,  73 
Geography,  Ptolemy's  work  on,  33  ;  Strabo 

on,  33 
Geology,  definition  of,  2  ;  of  Pythagoras, 
II,  215  ;  neglected  in  dark  ages,  214  ; 
Lazzaro  Moro  on,  216  ;  Werner  on,  217  ; 
Hutton  on,  219  ;  W.  Smith  on,  223  ;  Sir 
C.  Lyell  on,  405  ;  of  eighteenth  century, 
281  ;  prejudices  retarding,  404 
George   II.  founds  G5ttingen  University, 

196 
Geranium,    LInnseus's    definition    of    the, 

209 
Gerbert  introduces  Arabic   numerals    into 
Europe,  4$ 


GUTENBERG 

Germ,  growth  of  the,  141 
Germany,  Imperial  Academy  in,  126 
Gesner,  his  life  and  character,  65-70 ;  his 

cabinet  and  garden,   69  ;    his  history  ot 

animals,  69 ;  his  botanical  classification, 

70 
Gilbert,  first  experiments  on  electricity,  77, 

123 
Gioja  discovers  mariner's  compass,  53 
Glacial  period,  414 
Glacier,  term  explained,  411 ;  illustration 

of  a,  412;  of  Switzerland,  413;   carrying 

blocks  to  the  Jura,  413 
Gladstone,  Dr.,  his  life  of  Faraday,  349 
Glass,  angle  of  polarisation  of  light  from, 

310 ;  index  of  refraction  for,  108  ;  different 

dispersive  powers  of,  169 
Graham  on  variations  of  magnetic  needle, 

355 

Granite,  Hutton  on  formation  of,  221  ;  veins 
in  Glen  Tilt,  222 

Gravitation,  law  of,  explained,  148-155 ; 
discovered  by  Newton,  148  ;  its  action  on 
the  planets,  151  ;  attraction  acts  from 
the  centre  of  bodies,  150  ;  decreases  with 
the  square  of  the  distance,  152  ;  problems 
explained  by,  155  ;  holding  distant  stars 
together,  274 

Gravity,  action  of,  explained,  151 

Glen  Tilt,  granite  veins  in,  222 

Gnomon  at  Alexandria,  28 

Gold  separated  from  amalgam  by  Paracel- 
sus, 72 

Goethe  on  metamorphosis  of  plants,  381  ; 
on  discussion  between  Cuvier  and  St.- 
Hilalre,  395 

Gottingen  University  founded,  196 

Gough  the  patron  of  Dalton,  371 

Grsecus,  Marcus,  discovers  gunpowder,  42 

Gratz,  Kepler  professor  at,  95 

Greece,  Roman  conquest  of,  35 

Greek  colonies  in  Ionia,  8 

Greeks  deficient  in  natural  knowledge,  8 ; 
believed  the  sun  moved  round  the  earth, 
19  ;  knew  electric  nature  of  amber,  77  ; 
general  remarks  on  science  of  the,  34 

Grew  on  vegetable  anatomy,  141  ;  on 
stomates,  141 ;  on  cellular  tissue,  140 

Grove  cited,  434 

Guerlcke's  air-pump,  121  ;  Magdeburg 
hemispheres,  122 ;  first  electrical  ma- 
chine, 123  ;  his  experiments  on  electricity, 

124 
Gunpowder  known  to  the  Arabs,  42 
Gutenberg,  John,  the  printer,  55 


INDEX. 


459 


HALES 

HALES,  Dr.,  on  guses,  226  ;  on  water 
in  plants,  193 

Hall,  Mr.  C.  More,  on  flint  and  crown 
glass,  169 

Hall,  Sir  J.,  on  melted  rocks,  221 

Halle,  Dr.,  pleads  for  Lavoisier's  life,  239 

Haller,  early  life  of,  195  ;  his  work  with 
students,  196 ;  his  anatomical  plates,  196  ; 
on  contraction  of  the  muscles,  197  ;  on 
comparative  anatomy,  197 

Halley,  his  method  of  measuring  transits, 
158-162 ;  observes  transit  of  Mercury, 
158  ;  predicts  the  return  of  a  comet,  163 

Harding  discovers  Juno,  290 

Harvey  discovers  circulation  of  the  blood, 
no  ;  the  opposition  to  his  views,  113  ;  on 
development  of  the  chick,  113 

Hawksbee's  electrical  machine,  123 

Heat,  Bacon's  examination  of,  104 ;  early 
theories  about,  329  ;  produced  by  friction, 
330  ;  a  vibration,  333  ;  latent,  241,  334  ; 
mechanical  equivalent  of,  336 ;  Joule's 
experiments  on,  335-338  ;  conversion  of 
motion  into,  332-337  ;  converted  into 
motion,  338  ;  production  of  electricity  by, 
352 

Heat-rays  discovered,  315 

Heavy  bodies,  Galileo  on  motions  of,  82 

Helmholtz  cited,  434 

Hercules,  motion  of  our  solar  system  to- 
wards, 275 

Hermes  and  hermetic  philosophers,  41 

Hero's  engine,  245 

Herophilus  on  muscles,  nerves,  and  the 
pulse,  27 

Herschel,  SirW.,  makes  his  own  telescopes, 
272  ;  discovers  Uranus  and  receives  a 
pension,  272  ;  on  binary  stars,  273  ;  on 
star-gauging,  273  ;  on  nebulae,  274,  327  ; 
on  motion  of  solar  system  through  space, 
275  ;  discovers  heat-r«.ys,  315  ;  on  cause 
of  sun-spots,  353 

Herschel,  Sir  J.,  work  in  astronomy,  295- 
296  ;  on  Magellanic  clouds,  295  ;  his 
'  Outlines  of  Astronomy,'  296  ;  on  spec- 
trum analysis,  322 

Herschel,  Miss  C,  her  brother's  assistant, 
277 

Herschel,  Mr.  A.,  on  spectrum  of  falling 
stars,  328 

Hiero's  crown,  Archimedes  on,  23 

Higgins  on  chemical  law   of  proportions, 

373 
Hipparchus,   astronomy  of,   29 ;  discovers 

precession  of  equinoxes,  30 
Hippocrates  the  father  of  medicine,  14 


IRIDIUM 

Hirn,    M.,   his  experiments'  on  heat  con- 
verted into  motion,  338 
Hodgson,  Mr.,  on  outbreak  of  a  sun-spot, 

355 

Homology,  St.-Hilaire  on,  394 

Hooke  one  of  the  founders  of  the  Royal 
Society,  125  ;  on  air-pump,  128  ;  on  com- 
bustion, 130 ;  on  geology,  216 

Horrocks  observes  transit  of  Venus,  157 

Huen  island,  Tycho's  observatory  on,  78 

Huggins,  Dr.,  on  spectrum  analysis  of  the 
stars,  326  ;  of  nebulae,  327 

Human  anatomy,  Vesalius  on,  67 

Humboldt,  history  of,  384  ;  on  isothermal 
lines,  385  ;  on  distribution  of  plants,  385  ; 
his  '  Cosmos,'  386  ;  on  meteors,  297  ; 
pays  expenses  of  Agassiz's  work,  410 

Hunter,  John,  his  birth  and  history,  19S  ; 
on  comparative  anatomy,  198  ;  his  mu- 
seum, 199 

Hutton  on  geology,  219-23  ;  on  granite 
veins,  222  ;  and  Werner,  222 ;  on  size 
and  weight  of  Schehallien,  279 

Huyghens,  history  of,  175  ;  invents  cycloi- 
dal  pendulum,  175  ;  describes  Saturn's 
ring,  175  ;  his  undulatory  theory  of  light 
explained,  175,  181  ;  on  refraction  of 
light,  178  ;  on  double  refraction,  179 

Huxley  on  fossil  bird-reptile,  424  ;  on 
rapid  multiplication  of  plants,  429 

Hydrogen  discovered  by  Cavendish,  230 ; 
name  given  by  Lavoisier,  239  ;  amount 
of  in  water,  372 


ICE,  heat  lost  in  melting,    242  ;  melted 
by  friction,  333  ;  rocks  scratched  and 

blocks   carried   by,    413  ;  -period  in  the 

northern  hemisphere,  411 
Iceland  spar,  double  refraction  in,  180 
Igneous  rocks,  Hutton  on,  220 
Imperial  Academy  of  Germany  founded, 

126 
Index  of  refraction,  108 
Indians,  early  science  o^  4 
InductioD-coil,  351 
Inquisition   banishes   Vesalius,    68 ;   bums 

G.  Bruno,  83  ;  forces  Galileo  to  recant, 

93 
Insects,   Ray's  work  on,  144  ;  microscopic 

anatomy  of,  139 
Interference  of  light,  304-6 ;  colours  caused 

by,  307 
Invertebrate  animals,  Lamarck  on,  391 
Ionian  school  of  learning,  8 
Iridium  discovered,  323 


460 


INDEX, 


IRON 

Iron  tools  of  lake-dwellings,  417 
Islands,  formation  of,  12 
Isothermal  lines,  Humboldt  on,  3S5 
Italy,  early  scientific  societies  in,  126 


JAMES,  Sir  H.,  on  weight  of  the  earth, 
280 
Jansen  makes  a  telescope,  87 
Jews,  medical  knowledge  of  the,  39 
Joule,  Dr.,  experiments  on  the  mechanical 

equivalent  of  heat,  335-338 
Juno  discovered,  290 
Jupiter,    atmosphere  of,   327 ;   his  moons, 

90  ;  velocity  of  light  measured  by,  172  ; 

and  Saturn,  long  inequality  of,  269 
Jura  mountains,  erratics  of  the,  413 
Jussieu's  natural  system  of   plants,   211, 

382 


KENT'S  Hole,  flint  implements  in, 
416 

Kepler,  life  and  difficulties  of,  95,  loi  ;  on 
structure  of  eye,  96  ;  his  telescope,  97  ; 
his  first  law,  97  ;  second  law,  99  ;  third 
law,  100 ;  his  delight  at  Galileo's  dis- 
coveries, IOC ;  on  refraction,  100 ;  pre- 
dicted transits  of  Mercury  and  Venus, 
157 ;  finished  Rudolphine  tables,  loi  ; 
compared  with  Tycho  and  Galileo,  102 

Kew  gardens,  208 

Kircher  invents  magic  lantern,  76 

KirchhofF  on  dark  lines  in  solar  spectrum, 
323  ;  his  spectroscope,  324 

Kite,  Franklin's,  257 

Koran  forbade  dissection,  40 


LACTEALS     discovered    by    Asellius, 
114 
Lagrange,   266  ;  on  libration  of  the  moon, 

267 ;    on    stability    of   planetary  orbits, 

270 
Lake- dwellings  of _  Switzerland,  416;  tools 

and  food  found  in,  417 
Lamarck,  history  of,  389  ;  on  invertebrates, 

391  ;  on   development  of  animals,   391  ; 

his  'Philosophie  Zoologique,'  393  ;  weak 

point  in  his  theory,  393 
Lamont  on  variations  of  magnetic  needle, 

355 
Land,  conversion  of,  into  sea,  11 
Laplace,  267  ;  on  long  inequality  of  Jupiter 

and  Saturn,  269  ;  on  moon's  acceleration, 

270  ;  on  heat,  336 


LINN^US 

Lassell  on  Neptune's  moon,  295 

Latent  heat.  Black  on,  241 ;  of  water,  243  ; 
theory  of,  applied  by  Watt,  244,  248 ; 
explained,  334 

Latitude,  first  parallel  of,  laid  down,  27 

Laughing-gas,  Davy's  experiments  with, 
363   _ 

Lavoisier  the  founder  of  modem  chemistry, 
235  ;  his  experiments,  237  ;  his  death,  239 

Law  of  compressibility  of  gases,  128  ;  of 
definite  proportions  in  chemistry,  372  , 
of  multiple  proportions,  373  ;  of  gravita- 
tion, 151  ;  of  refraction  discovered  by 
Snellius,  107 

Laws  of  Kepler,  97,  99,  100 

Leaves  of  plants.  Bonnet  on  use  of,  200 

Leeuwenhoeck  on  animalcules,  139 

Leibnitz  on  differential  calculus,  148 

Lenses,  magnifying  power  of  convex,  49  ; 
Alhagen  on  use  of,  48  ;  Porta  on,  76  ; 
Galileo  on,  88  ;  Kepler  on,  96 

Leslie,  Sir  J.,  on  refraction  of  heat,  340 

Lever,  Archimedes  on  the,  22 

Leverrier  calculates  the  position  of  Nep- 
tune, 292,  294 ;  on  November  meteors, 
299 

Leyden,  medical  school  of,  190 

Libration  of  the  moon,  267 

Liebig  on  organic  chemistry,  377 

Light,  Euclid  on  rays  of,  21 ;  a  vibration, 
176  ;  causing  colour,  177  ;  polarization 
of,  181,  309  ;  compared  to  sound,  176, 
178  ;  dispersion  of,  164,  167  ;  blending 
of  colours  into  white,  168  ;  interference 
of,  302-306  ;  bands  of,  in  shadows,  304  ; 
undulations  compared  to  waves  of  a 
pond,  306 ;  reflection  of  from  a  soap- 
bubble,  308  ;  complex  vibrations  of,  312  ; 
passage  of  through  a  crystal,  313 ; 
Roemer  measures  velocity  of,  172 ;' 
theories  of,  174,  .303  ;  undulatory  theory 
explained,  174-179 

Lightning,  electric  nature  of  proved  by 
Franklin,  256  ;  conductors,  258 

Lilienthal,  meeting  of  astronomers  at,  289 

Limestone,  fixed  air  obtained  from,  226 ; 
beds  of  Sicily,  thickness  of,  407 

Lines  in  the  spectrum,  318,  320 ;  their 
cause  explained,  323 

Linnsean  system,  210;  collection  brought 
to  England,  212 

Linnaeus,  early  life  of,  205,  207  ;  and  BufFon 
compared,  207  ;  his  '  Excursions,'  208  ; 
gives  specific  names  to  plants  and 
animals,  208  ;  creates  an  accurate  nomen- 
clature,   211  ;    modifies    Ray's    system. 


INDEX. 


461 


LIPPERSHEY 

145  ;  on  metamorphosis  of  plants,  383  ; 
death  and  character  of,  212 
Lippershey  makes  a  telescope,  87 
Lithuanian  legend  about  falling  stars,  297 
Loadstone  known  to  the  Greeks,  53 
Locke  on  heat,  330 

Lockyer  on  spectrum  analysis  of  stars,  326 
Locomotive-engine,  date  of  first,  245 
Looking-glass,  cause  of  reflection  of,  177 
Lungs,  circulation  of  blood  through  the, 

112  ;  studied  by  Malpighi,  T38 
Luxembourg    Palace,   polarized    light  re- 
flected from  windows  of,  310 
Lyell,  Sir  C,  his  history,  405  ;  on  present 
causes  of  geological  change,  406-410  ;  his 
influence  on  geology,  409  ;  on  Darwin's 
work,  426 
Lymphatics  discovered  by  Riidbeck,  1 15 . 


MAC  ENERYon  flint  implements  of 
Kent's  Hole,  416 

Magdeburg  hemispheres,  122 

Magellan's  ship  sails  round  the  world,  57 

Magellanic  clpuds,  295 

*  Magia  Naturalis  '  published,  74 

Magic  lantern  invented,  76 

Magnet,  origin  of  name,  53  ;  producing 
electric  current,  350  ;  and  electric  wires, 
mutual  rotation  of,  349 ;  diagram  of, 
350 

Magnetic  currents  caused  by  electric  cur- 
rents, 346  ;  direction  of,  345  ;  affected  by 
sun-spots,  355  ;  needle,  variations  of  the, 
57 ;  affected  by  electric  current,  343, 
345  ;  Ampere  on  direction  of,  345  ;  sudden 
movement  of  at  Kew,  355  ;  periodical 
shifting  of  the,  355  ;  of  electric  telegraph, 

359 
Magnetism,  Gilbert  on,  77 ;  electro-,  341- 
352 ;   terrestrial    affected    by  sun-spots, 

353 

Magnifying  glasses  explained,  49 

Malpighi  applies  the  microscope  to  living 
structures,  137  ;  history  of,  13S  ;  on  air- 
cells,  138  ;  discovers  Malpighian  layer, 
139 ;  on  silkworm,  139 ;  on  structure  of 
plants,  140 ;  on  growth  of  germs  and 
seeds,  141 

Malus  on  polarization  of  light,  309 

Man,  antiquity  of,  413  ;  selection  of  animals 
by,  428 

Map  made  by  Anaximander,  10  ;  geologi- 
cal, made  by  W.  Smith,  224 

Marcus  Grsecus,  gunpowder  made  by,  43 

Mariner's  compass,  53 


MOON 

Marquis  of  Worcester's  engine,  246 

Marriotte's  law,  130 

Mars,   atmosphere  of,  327  ;  movements  of 

explained  by  Kepler,  97  ;  occultation  of 

observed  by  Aristotle,  16 
Maskelyne  measures    the    density  of   the 

earth,  277 
Maury  on  division  of  Biela's  comet,  292 
Mayer,  Dr.,  on  mechanical  equivalent  of 

heat,  335 
Mayow  a  conscientious  observer,  131  ;  he 

discovers  'fire-air,'  132  ;  his  experiments 

on  combustion  and  respiration,  132  ;  his 

early  death  prevented  his  theory  being 

known,  135 
'  Mecanique  Celeste '  of  Laplace,  271 
Mechanical  equivalent  of  heat,  336 
Mechanics,  definition  of,  2 
Medical  school  of  Leyden,  190 
Medicine,  Hippocrates  the  father  of,    14 ; 

Galen  on,  34 
Melloni  on  passage  of  heat  rays,  340 
Men    of  science,   lists  of,   6,    38,    62,    86, 

188 
Mercurial  thermometer,  how  made,  120 
Mercuric  oxide,  Priestley  obtains  oxygen 

from,  233 
Mercury  obtained  from  cinnabar  by  Geber, 

44  ;  sustained  in  a  tube  by  weight  of  air, 

118  ;  combining  with  ox3'^gen,  373 
Mercury,  transits  of  observed,  157-158 
Metals,  Geber  notices  increased  weight  of 

heated,  44  ;    electric  discharge  from  two, 

261 ;    discovered  by  spectrum   analysis, 

322 
Metamorphosis  of  plants,  381 
Meteors  and  their  paths,  297-300 ;    their 

composition,  297  ;  spectrum  analysis  of, 

328 
Microscope    applied   to  living  structures, 

137  ;  definition  of,  137 
Middle  ages,  science  of  the,  39-59 
Milky  Way  studied  by  Democritus,  15  ; 

by  Galileo,  90 
Miller,   Dr.,  on  spectrum  analysis   of  the 

stars,  326 
Mineral   waters  analysed  by  Bergmann, 

229 
Mineralogy,    Gesner    on,    70 ;     Werner's 

lectures  on,  217 
MoUusca,  term  explained,  396 
Monocotyledons,  term  explained,  145 
Monro  cited,  380 
Mont  Blanc,  erratic  blocks  carried  from, 

413 
Moon,  Anaxagoras  on  the,   13  ;  phases  of 


462 


INDEX. 


MOONS 

explained  by  Anaximander,  10 ;  Thales 
on  reflection  of  the,  9  ;    secondary  light 
of  the,  89  ;  movement  of  used  by  New- 
ton to  test  his  law  of  gravitation,  150  ; 
Lagrange  on  libration  of,  267  ;  why  she 
turns  the  same  face  to  us,  268 
Moons,  Jupiter's,  90 
Moraines  of  glaciers,  412 
Moro,  Lazzaro,  on  formation  of  strata,  216 
Morse,  his  electric  telegraph,  356,  361 
Mother-of-pearl,  cause  of  colours  in,  309 
Motion,  conversion  of,  into  heat,  332,  337 
Mountain-chains,  Eratosthenes  studies,  29 
Mouse  consuming  air  in  a  bell-jar,  132 
Mud  carried  down  by  the  Ganges,  407 
Murchison  cited,  407 

Muscles,  Haller  on  contraction  of  the,  197 
Musical  notes,  Pythagoras  on,  12 


ATAPOLEON  I.    takes  St.-Hilaire  to 

-i M      Egypt,  391 

Natural  history  of  seventeenth    century, 

137-145   .  .     . 

Natural  philosophy,  Leonardo  da  Vmci  on, 

58 

Natural  selection,  theory  of,  426-428  ;  ob- 
jection to  the  theory  of,  428  ;  difficulties 
of  natural  history  explained  by,  431  ; 
does  not  exclude  Divine  Power,  432 

Natural  system  of  plants,  211,  382 

Nebulae,  Herschel  on  the  nature  of,  275  ; 
spectrum  analysis  of,  327 

Nebular  hypothesis,  271 

Negative  and  positive  electricity,  256,  262 

Negro,  colouring  matter  in  skin  of,  139 

Neptune,  position  of  found  by  Adams  and 
Leverrier,  292  ;  seen  by  Galle,  294 ;  his 
moons,  295 

Neptunists  and  Vulcanists,  218 

Nerves,  Galen  on  two  sets  of,  34 

Nestorians,  science  of  the,  40 

Neuchatel,  erratic  block  near,  413 

Newcomen's  engine,  246 

Newt,  re-growth  of  eye  of,  202 

Newton,  birth  and  early  life  of,  14 ;  his 
law  of  gravitation,  148-155,  183  ;  his 
method  of  fluxions,  148  ;  on  variation  of 
attraction,  152  ;  on  cause  of  tides,  154  ; 
on  specific  gravity  of  planets,  154  ;  01^ 
shape  of  the  earth,  154  ;  on  precession  of 
equinoxes,  154;  on  motion  of  comets, 
155  ;  on  sound,  175  ;  on  chemical  attrac- 
tion, 229 ;  on  attraction  of  plumbline  to 
a  mountain,  278 ;  on  light  and  colour, 
148  ;  on  dispersion  of  light,  164,  185    ex- 


PAPIN 

plains  the  spectrum,  166  ;  and  compound 
nature  of  light,  165-167  ;  his  rotating 
disc,  168 ;  his  work  on  chemistry  de- 
stroyed, 170 ;  his  work  on  optics,  169  ; 
his  theory  of  light,  174,  303  ;  his  charac- 
ter and  death,  170 

Newton,  Prof.,  on  falling  stars,  229 

Nicholson  on  decomposition  of  water  by 
electricity,  364 

Nile,  mud  carried  down  by,  11 

Nineteenth  century,  tendency  of  science  of, 

434 
Nitrogen,  compounds  of  oxygen  with,  373 ; 

Rutherford  on,  235 
Nitrous  oxide,  Davy's  experiments  on,  363 
Nobili  on  animal  electricity,  261 
'  Novum  Organum,'  103 
Numerals,  Indian,  introduced  into  Europe, 

46    _ 
Nutation  of  earth's  axis,  266 


OBLIQUITY  of  ecliptic,  Anaxagoras 
on,  21 
Observatory,  Tycho's,  79 
Oersted  on  electro-magnetism,  341 
Olbers,  Dr.,   discovers  Pallas  and  Vesta, 

290 
Optics,   Alhazen   on,    46 ;    Porta  on,    76 ; 

Kepler  on,  96  ;  Newton's  work  on.  169 
'Opus  Majus '  of  Roger  Bacon,  51 
Orbits  of  the  planets,  elliptical,  98  ;  do  not 

all  lie  in  the  same  plane,  99 ;  governed 

hy  gravitation,  151 
Organic    chemistry,   foundation   of,    190  ; 

Liebig  on,  377 
Organic  sciences  of  nineteenth  centui-y  too 

difficult  to  follow,  380 
Organs,  of  digestion  arranged  by  Hunter, 

199  ;  modification  of,  381 ;  St.  Hilaire  on 

modification  of,  393 
*  Ossemens  Fossiles '  published,  399 
Ovid's  'Metamorphoses,'  11 
Oviparous  and  viviparous  animals,  143 
Oxford,  early  meetings  of  Royal  Society 

at,  125 
Oxygen  called  '  fire-air '  by  Mayow,  134  ; 

discovered  by  Priestley  and  Scheele,  231- 

234  ;  amount  of  in  water,  372  ;  compounds 

of  with  nitrogen,  373 


I'^ADUA,  Professors  of,  67,  71,  81,  no 
Palissy  on  fossil  shells,  215 
Pallas  discovered,  290 
Papin's  engine,  246 


INDEX. 


46J 


PARABOLAS 

Parabolas  described  by  comets,  155 

Paracelsus,  chemistry  of,  72 

Paris,  Cuvier  on  fossil  animals  of,  397 

Pascal  on  pressure  of  the  amosphere,  119 

Pecquet  on  thoracic  duct,  114 

Pericles  pleads  for  Anaxagoras,  14 

Perrier,  M.,  carries  a  barometer  up   the 

Puy  de  Dome,  119 
Pendulum,  Galileo  on  the,  79 
Phases  of  moon,  10  ;  of  Venus,  91 
Philosopher,   name  first  given  to  Pytha- 
goras, 12 
Philosophical  transactions  begun,  127 
Phlogiston,  theory  of,   135  ;   destroyed  by 

Lavoisier,  238 
Photography  explained,  317 
Physics,  definition  of,  2  ;  of  sixteenth  cen- 
tury,   83  ;  of  seventeenth  century,  114  ; 
of  eighteenth  century,  282 
Physical,  forces,  correlation  of  the,   435  ; 

geography,  Humboldt  on,  386 
Physiology,   beginning  of   the    study  of, 

110-115 
Piazzi  discovers  Ceres,  289 
Picart,  size  of  the  earth  measured  by,  150 
Pierre-a-Bot,  an  erratic  block,  413 
Pigeons,    common     descent     of    different 

varieties  of,  392 
Pisa,  Galileo  and  the  men  of,  81 
Pith  of  elder,  cells  in,  140  ;  ball  attracted 
and  repelled  by  rubbed  sealing-wax,  124 
Planets,  Anaxagoras  on,  14  ;  Eudoxus  on, 
^,        15;  Kepler's  laws  concerning  the,  97- 
K      100  ;  held  in  their  orbits  by  gravitation, 
H      rsi  ;  minor,  or  asteroids,  289 ;  stability 
B     of  their  orbits  proved  by  Lagrange,  270  : 
^     their    weight    and    size    calculated    by 
Leverrier,  294 
Plants,  Aristotle  on  low  organisation  of, 
16  ;   Theophrastus  on,   17  ;   microscopic 
structure  of,  140 ;   ashes  of,  examined  by 
^      Boerhaave,  193  ;   Hales  on  breathing  of, 
^^  193  ;  Bonnet  on  leaves  of,  200 ;  Gesner 
^^t  on,  70;  Csesalpinus  on,  71 ;  Ray  on,  142  ; 
^H>  Linnseus,     artificial     system     of,     208 ; 
^^  Jussieu,    natural  system  of,    211,   382  ; 
specific  names  given  to,  209  ;    Humboldt 
on  distribution  of,  385  ;  metamorphosis 
of,  381  ;  Priestley  on  breathing  of,  232 
Playfair's  illustrations  of  Hutton,  219 
PolarizsSion  of  light,   181 ;   by  reflection, 

309 ;  circular,  314 
Porta,   his  meetings  in   Naples,    74 ;    his 
camera  obscura,  75  ;  on  the  eye,  76 ;  his 
engine,  246 
Positive  and  negative  electricity,  256,  262 


RED 

Potassium  discovered  by  Davy,  365 
Potter,  Humphrey,  ties  the  engine-cocks 

247 
Ptolemaic  system,  32 
Ptolemies  patrons  of  learning,  18 
Ptolemy,  astronomy  of,  32  ;  geography  of, 

33  ;  'cloudy  stars  '  seen  by,  274 
Precession    of    equinoxes    discovered    by 

Hipparchus,  30 ;  Newton  on,  154 
Pressure  and  volume,  relations  of,  130 
Prestwich  on  flint  implements,  416 
Priestley,  his  discoveries,  232  ;  calls  oxygen 
'  dephlogisticated  air,'  234  ;  his  troubles 
and  death,  235 
Prism,  light  dispersed  in  a,  165 
Prismatic  colours,  Newton  on,  167 
'  Principia,'  some  problems   discussed    in 

the,  153 
'  Principles  of  Geology  '  published,  410 
Printing,  invention  of,  55 
Proctor  on  shooting  stars,  299 
Proportions,  law  of  definite,  373 
Proust  on  chemical  law  of  proportions,  373 
Pulmonary  circulation  of  the  blood,  113 
Pulse  studied  by  Herophilus,  27 
Pump,  height  that  water  will  rise  in,  117 
Pythagoras,  science  of,  11,  215 
Pythagorean  system,  21 


QUADRANT  made  by  Copernicus,  (i() 
Quadrupeds,  Ray's  work  on,  143 
Quicklime,  nature  of,  226 


RABBITS    descended    from    one   wild 
stock,  392 
Radiata,  term  explained,  396 
Rain,  denuding  effects  of,  406 
Rainbow,  De  Dominis  on,  164 
Ramsay,  Prof.,  cited,  218 
Ray,   on  geology,    216 ;  and  Willughby, 
history  of,  142  ;  on  quadrupeds,  143  ;  on 
birds,  fishes,  and  insects,  144  ;  on  plants, 

145 
Rays  of  light,  index  of  refraction  of,  108  ; 
Euclid  on,  21 ;  Alhazen  on  refraction  of, 
47  ;  Kepler  on,  96 ;  Young  and  Fresnel 
on,   305-309  ;    Newton  on  refraction  of 
coloured,  166 ;  non-interference  of  ordi- 
nary and  extraordinary,    312 ;  paths  of 
through    a    crystal,    313 ;    discovery  of 
chemical  and  heat,  315 
Reaumur's  scale,  freezing  point  of,  120 
Red  fire  made  by  burning  strontium,  322 


464 


INDEX. 


REFLECTION 

Reflection  of  light,  177  ;  polarization  of 
light  by,  309 

Refraction  explained  by  Alhazen,  47  ;  ex- 
plained by  Huyghens,  178  ;  figures  illus- 
trating, 179  ;  double,  179,  180 ;  Snellius 
discovers  law  of,  106  ;  method  of  mea- 
suring,   108 ;     of    coloured    rays,    166 ; 

'Regne  Animal,' Cuvier's,  397 

Reptiles,  gigantic  fossil,  423 

Repulsion  by  electricity,  124 

Respiration,  Boyle  on  air  used  in,  131  ; 
Mayow  on  effects  of  fire-air  in,  134 

Richter  on  chemical  law  of  proportions, 
373  ;  and  Reich  discover  iridium,  323 

Rieban,  Mr.  Faraday's  master,  348 

Ritter  discovers  chemical  rays,  315 

Rivinus  on  plants,  209 

Robison  on  Watts,  245 

Rocks,  diagrams  of,  bent  and  broken,  218  ; 
new  ones  formed  out  of  old,  220 

Roe  of  codfish,  animalcules  in,  140 

Roemer  measures  velocity  of  light,  172 

Roger  Bacon  makes  gunpowder,  52 ;  his 
experiments  on  air,  52 

Ronald's,  Mr.,  attempt  at  electric  tele- 
graph, 356 

Rose,  modification  of  parts  in  the,  382  ; 
number  of  species  of,  420 

Rothmann,  Dr.,  befriends  Linnseus,  205, 
207 

Royal  Institution,  Young  professor  at,  303  ; 
Davy  at,  363  ;  Faraday  at,  348 

Royal  Society  founded,  125  ;  early  mem- 
bers of,  127  ;  Newton  learns  tlie  real 
size  of  the  earth  at  the,  150 ;  Halley's 
method  proposed  to  the,  158 

Rubidium  discovered,  323 

Rudbeck  discovers  lymphatics,  115 

Rudimentary  organs,  421 

Rudolph  II.  protects  Tycho  and  Kepler, 

79.  95  _ 

Rudolphine  tables,  79,  loi ;  used  to  pre- 
dict transits,  157 

Rumford,  Count,  his  history,  330 ;  pro- 
duces heat  by  friction,  331  ;  appoints 
Davy  to  Royal  Institution,  363 

Rutherford,  Dr.,  on  nitrogen,  235 


SABINE,  Sir  E.,  on  connection  between 
sun-spots  and  magnetic  currents,  355  ; 
on  weight  of  our  earth,  280 
St.-Hilaire,  G.,  history  of,  390  ;  on  Egyp- 
tian animals,  391  ;  on  homologous  parts 
of  animals,  393 ;  his  discussion  with 
Cuvier,  395 


SLOUGH 

Salamanders,  regrowth  of  limbs  of,  201 

Sal-ammoniac  known  to  the  Arabs,  45 

Salerno,  medical  school  of,  40 

Salt,  colour  of  burning,  322 

Salts  of  plants  extracted,  193 

Sap,  Ray  and  Willughby  on,  143 

Satellites  of  Jupiter,  90 ;  eclipses  of,  173 

Saturn,  atmosphere  of,  327  ;  weight  of,  154 ; 
his  ring  seen  by  Galileo,  92  ;  and  Jupiter, 
long  inequality  of,  269 

Saussure,  De,  on  glaciers,  412 

Savery's  engine,  246 

Scheele,  discoveries  of,  232  ;  on  chemical 
rays  of  light,  316 

Schehallien  experiment,  277  ;  diagram  of, 
279 

Schiaparelli  on  August  meteors,  298 

Schoeffer,  Peter,  the  printer,  55 

Schwabe  on  periodicity  of  sun-spots,  354 

Science,  definition  of,  1  ;  of  the  Greeks, 
7  ;  decay  of  Greek,  35  ;  of  the  Middle 
Ages,  39,  59  ;  of  the  Arabs,  39,  50  ;  rise 
of  modem,  63  et  seq.  ;  of  sixteenth  cen- 
tury, 82 ;  seventeenth  century,  182 ; 
eighteenth  century,  280 ;  academies  of, 
124 ;  lists  of  chief  men  of,  6,  38,  62,  86, 
188,  286 

Scilla  on  Calabrian  fossils,  216 

Scotland,  glaciation  of,  414 

Screw  of  Archimedes,  25 

Sea,  land  eaten  away  by  the,  406,  408 

Seasons  caused  by  obliquity  of  ecliptic,  20 

Section  of  the  skin,  139 

Seebeck,  Professor,  discovers  thermo-elec- 
tricity, 352 

Seeds  and  germs,  growth  of  compared, 
141 ;  classification  of  plants  by,  71 

Seguin,  M.,  on  mechanical  equivalent  of 
heat,  335 

Selection  of  animals  by  man,  428 ;  Natural, 

429        _ 
Serapis,  rise  and  sinking  of  temple  of,  408 
Seirvetus  on  circulation  of  blood,  iii 
Seventeenth  century,   characteristic  work 

of,  433  ;  summary  of  science  of  the,  182, 

186 
Shooting-stars,  a  legend  concerning,  297 
Sicily,  thickness  of  limestone  rocks  in,  407 
Silkworm,  Malpighi  on  structure  of,  139 
Simpson,  Dr.,  on  chloroform,  378 
Sines  of  incident  and  refracted  rays,  109 
Sixteenth  century,  advance  of  science  in 

the;  82,  433 
Skaptar  Jokul,  torrent  of  lava  from,  408 
Skin,  section  of,  139 
Slough,  Herschel's  observatory  at,  273,  295 


INDEX. 


465 


SMITH 

Smith,  Sir  E.,  brings  Linnsean  collection 

to  England,  213 
Smith,  William,  surveys  England,  223 
Snails,  regrowth  of  parts  in,  201 
Snellius  discovers  law  of  refraction,  106 
Soap-bubble,  Newton  on  the,  169  ;  cause 

of  colours  on  the,  307 
Soda,  composition  of,  376 
Sodium  discovered  by  Davy,   365  ;  power 

of  to   decompose  water,   375 ;  spectrum 

of,   322  ;    KirchhofTs  experiments   with 

vapour  of,  325 
Soho,  manufactory  of  engines  at,  251 
Soil,    substances    taken    from  by  plants, 

193 

Solar,  spectrum,  dark  lines  in,  318  ;  and 
star-spectrum  compared,  321  ;  system, 
motion  of  through  space,  275 

Solstices  observed  by  Thales,  9 

Sound,  Newton  on,  175  ;  light  compared 
to,  176,  178 

Spallanzani  on  regrowth  of  severed  limbs, 
201 

Specific  gravity  first  measured  by  Archi- 
medes, 23 

Specific  names  given  by  Linnseas,  208 

Sptctra,  table  of,  320 

Spectrum  studied  by  Newton,  165  ;  dark 
lines  on  the,  318,  320  ;  their  cause  ex- 
plained, 323  ;  of  different  substances, 
321  ;  of  gases,  322  ;  of  solids,  322 

Spectrum  analj'sis,  history  of,  315-28 : 
metals  discovered  by,  323  ;  of  sunlight, 
323  ;  of  stars,  326  ;  of  nebulae,  327  ;  of 
meteors,  328  ;  use  of  in  chemistry,  370 

Spencer,  Herbert,  on  evolution,  435 

Spirit,  Arabian  name  for  gas,  42 

Spirits  of  wine  made  by  Geber,  44 

Spots  on  the  sun,  periodicity  of,  354 

Stahl's  work  in  chemistry,  135  ;  on  phlo- 
giston, 135 

Ctar,  morning  and  evening,  11  ;  -clusters 
and  nebulas,  Herschel  on,  274  ;  -gauging 
by  Sir  W.  Herschel,  273 

Stars,  binary,  273  ;  spectrum  analysis  of 
the,  326 

Statics,  Stevinus  on,  82 

Steam,  condensation  of,  249  ;  latent  heat 
of,  243 

Steam-engine,  history  of  the,  245 ;  New- 
comen's,  246  ;  Watt's,  249 

Steinheil  on  electric  telegraph,  357;  on 
earth  acting  as  return  wire,  358 

Steno  on  fossils  in  the  earth's  crust,  215 

Stereoscope,  Sir  J.  Herschel  on  the,  320 

Stevinus  on  statics,  82 


THERMOMETER 

Stokes,   Professor,  on  dark  lines  in  solar 

spectrum,  323 
Stomachs  of  animals,  peculiarities  of,  199 
Stone  tools  of  lake-dwellings,  417 
Strabo  on  earthquakes  and  volcanoes,  33 
Strata  of  England  mapped  by  W.  Smith,  223 
Striae  caused  by  glaciers,  413 
Struve  on  Neptune's  moons,  295 
Sublimation  described  by  Geber,  44 
Suction-tube,  section  of  a,  117 
Sulphuric  acid  made  by  Geber,  45 
Summary  of  science  of  sixteenth  century, 
82 ;    of   seventeenth    century,    182 ;    of 
eighteenth  century,  280 
Sun,  experiment  to  explain  the  movement 
of  the  earth  round  the,    19 ;  seen  after 
setting  by  means  of  refraction,  48 ;  ro- 
tation on  its  axis  proved  by  Galileo,  92  ; 
his  distance  108  times  his  diameter,  159  ; 
method  of  measuring  the  diameter,  159- 
161 ;  distance  from  the  earth,  162  ;  holds 
the  planets  round  It  by  gravitation,  152  : 
meteors  falling  into,  300 ;  atmosphere  of 
vapours  surrounding  the,  325  ;  spectrum 
of  the  light  of,  318 
Sun-dial  invented  by  Anaximander,  10 
Sun-spots  seen  by  Galileo  and  Harriot,  92  ; 
Sir    W.    Herschel    on    cause    of,    353 ; 
Schwabe   on   periodicity  of,    354 ;  their 
connection  with  magnetic  currents,  355 
Switzerland,    glaciers   of,    412 ;    lake-dwel- 
lings of,  416 
Syene,    earth's     circumference     measured 

from,  29 
Syntaxis  of  Ptolemy,  32 
Synthesis,  term  explained,  371 
'  System  of  the  World,'  by  Galileo,  93 
'  Systema  Naturae '  published,  211 

TALBOT,  Fox,  on  sun-pictures,  317  ;  on 
spectra  of  flames,  323 
Telegraph  (see  electric  telegraph) 
Telescope,  Roger  Bacon's  idea  of,  52  ;  in- 
vention of  the,  87  ;  Galileo's,  89  ;  Kepler's, 
97  ;  achromatic,  169 
Tessier,  Abbe,  meets  Cuvier,  390 
Tests,  Bergmann  on  chemical,  229 
Thales,  science  of,  8 
Thallium  discovered,  323 
Theophrastus  the  first  botanist,  17 
Theories  about  living  beings,  381 
Theory  of  the  '  Earth '  published,  219 
Thermo-electricity,  discovery  of,  352 
Thermometer,  invention  of  the,  lac 


466 


INDEX. 


THOMPSON 

Thompson,  Benjamin  {see  Rumfoi'd) 
Thomson,    Dr.,    on  Dalton's  theory,  377  ; 

Sir  W.  cited,  323,  434 
Thoracic  duct,  Pecquet  on  the  use  of,  114 
Tides,  Newton  on  cause  of,  155 
Torricelli  on   weight   of  atmosphere,  117  ; 

invents  barometer,  118 
Torricellian  vacuum,  119 
Tournefort's  classification  of  plants,  145 
Tower,  Hunter  dissects  the  wild  beasts  of 

the,  198 
Transits   of  Mercury  and  Venus,  156-63  ; 

Halley's  method  of  measuring,  160  ;  De- 

lisle's  method   of  measuring,  266;  dia-* 

grams  of,  160^61  ;  expeditions,  162 
Transparency  of  glass,  cause  of,  177 
Trianon,  Jardin  de,  208 
Truth,  our  want  of  faith  In  the  power  of, 

436 
Tycho  Brahe,  his  life    and    astronomical 

work,  78  ;  Galileo  and  Kepler  compared, 

102 
Tychonic  system,  78 
Tylor,  E.  B.,  illustrations  of  refraction  of 

light,  178 
Tjmdall,  Dr.,  on  heat,  340 


UNDULATORY  theory  of  light,  175, 
303  ;  explains  Interference,  305 
Uniform  action  of  geological  change,  409 
Upsala,   Linnseus's  botanical    garden    at, 

208 
Uranlenburg,  Tycho's  observatory  at,  79 
Uranus,    discovery  of,  272;   its    irregular 
movements  lead  to  discovery  of  Neptune, 
292-294 


T  7ACUUM,  Torricellian,  119 
»       Valleys,  excavation  of,  11 
Valves  in  veins  discovered  by  Fabricius, 

III  ;  use  of,  112 
Van  Helmont,  chemistry  of,  72 
Varieties,  useful  ones  alone  survive,  430 
Vasco  de  Gama  sees  southern  stEirs,  57 
Vegetable  anatomy,  140 
Veins,  Galen  on,  34  ;  action  of  discovered 

by   Harvey,  iii;  valves  in,    discovered 

by  Fabricius,  in 
Velocity  of  light  measured,  172 
Venus,  phases  of,  agree  with  Copernican 

theory,  91 
Venus,  transits  of,    147  ;   used  to  measure 

sun's  distance,  158  ;  Halley's  method  of 

measuring,   160  ;     diagrams  illustrating. 


WILLIAM 

159,    160,    161 ;      Delisle's     method    of 

measuring,  266 
Vertebrata,  term  explained,  396 
Vesalius,  his  work  in  anatomy,  67 ;  ban- 
ishment and  death  of,  68 
Vessels  and  fibres  of  plants,  140 
Vesta  discovered,  290 
Vibrations,  light  a  series  of,  176  ;  of  light 

complex,  313 
Vinci,  Leonardo  da,  inventions  of,  58 
Vital  fluids,  belief  of  alchemists  in,   192  ; 

spirits,  belief  in,  no 
Vitelllo  on  refraction,  106 
Viviparous  and  oviparous  animals,  143 
Volcanoes,   Pythagoras  on,    12  ;    mass  of 

lava  throv/n  out  from,  408 
Voltaic  electricity,  261  ;  pile,  263 
Volta  on  electricity,    261 ;    his  crown    of 

cups,  262  ;  his  controversy  with  Galvani, 

260 
Volume  and  pressure,  relations  of,  130 
Von  Baer  on  embryology,  400 
Voyages  round  the  world,  56 
Vulcan,  god  of  volcanoes,  7 
Vulcanists  and  Neptunlsts,  218 


WALES,  moraines  and  erratic  blocks 
of,  44 

Wallace,  Mr.  A.  R.,  figures  drawn  by,  97  ; 
on  natural  selection,  425,  426 ;  on  pro- 
lificness  of  birds,  429 

Wallis,  Dr.,  his  description  of  the  Royal 
Society,  125 

Water,  composition  of,  231,  239,  372  ; 
rising  in  a  vacuum,  117  ;  latent  heat  of, 
243  ;  boiled  by  friction,  332  ;  rise  of 
temperature  in  by  friction  calculated, 
336  ;  decomposed  by  sodium,  375 

Watt,  his  early  life,  244  ;  not  the  first  to 
make  a  steam-engine,  245  ;  his  separate 
condenser,  248  ;  his  double-acting  engine, 
250  ;  his  partnership  with  Boulton,  251 

Wave-theory  of  light,  175  ;  explains  inter- 
ference, 305 

Waves  of  light  in  a  crystal,  313 

Wedgwood,  Dr.  T.,  on  sun-pictures,  317 

Weight  of  bodies  explained  by  gravitation, 
154  ;  of  chemical  elements,  373 

Wenzel  on  law  of  definite  proportions,  373 

Werner  on  rocks  and  fossils,  217 

Westminster  Abbey,  Newton  buried  in, 
171 

Wheatstone  patents  electric  telegraph,  357 

William  of  Orange  founds  Leyden  Univer- 
sity, 191 


4 


INDEX. 


467 


WILLUGHBY 

Willughby  and  Ray,  142 ;  death  of,  143  ; 

on  classification  of  animals,  143 
WoKler  on  organic  chemistry,  377 
Wolff  on  metamorphosis  of  plants,  383 
Wollaston,  Dr.,  observes  dark  lines  in  the 

spectrum,  318 
Woodward,  his  geological  collection,  216 
Woolsthorpe,  birthplace  of  Newton,  147 
World,  first  voyages  round  the,  56 
Worm,  regrowth  of  divided  parts  of  the. 


ZOOLOGY 

YEAR,  length  of  calculated,  45 
Young,  Dr.,  his  life,  303  ;  on  inter- 
ference of  light,  304-306  ;  and  Fresnel  on 
polarisation  of  light,  311 


ZODIAC,  or  circle  of  animals,  19 
Zoology,  Aristotle  on,  16 ;  Gesner  on, 
69  ;  Ray  and  Willughby  on,  143  ;  Lin- 
naeus on,  210 ;  Cuvier,  St.-Hilaire,  and 
Goethe  on,  391  et  seg.  ;  Darwin  on,  426 


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Prof.  RUDOLPH  VIRCHOW  (Berlin  University).     Morbid  Physiological  Action. 
Prof.  CLAUDE  BERNARD.     History  of  the  Theories  of  Life. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


THE  INTERNATIONAL  SCIENTIFIC  SERIES. 


FORTHCOMING    VOLUMES. 

^^£  H.  SAINTE-CLAIRE  DEVILLE.     An  Introduction  to  General  Chemistry, 

Prof.  WURTZ.     Atoms  and  the  A  tojnic  Theory, 

Prot  De  QUATREFAGES.     The  Human  Race. 

Prof.  LACAZE-DUTHIERS.     Zoology  since  Cuvier. 

Prof.  BERTHELOT.     Chemical  Synthesis. 

Pro£  C.  A.  YOUNG,  Ph.  D.  (of  Dartmouth  College).     The  Sun. 

Prof:  OGDEN  N.  ROOD  (Columbia  CoUege,  N.  Y.).    Modern  Chromatics  and  its 

Relations  to  A  rt  and  Industry, 
Dr.  EUGENE  LOMMEL  (University  of  Eriangen).     The  Nature  of  Light. 
prof.  J.  ROSENTHAL.     General  Physiology  of  Muscles  and  Nerves. 
Prof.  JAMES  D.  DANA,  M.  A.,  LL.  D.     On  CeJ>halization ;  or.  Head-character* 

in  the  Gradation  and  Progress  of  Life. 
Prof  S.  W.  JOHNSON,  M.  A.     On  the  Nutrition  of  Plants. 

Prof  AUSTIN  FLINT,  Jr.,  M.  D.  The  Nervous  System,  and  its  Reuition  to  ike 
Bodily  FunctioTis. 

Prof.  BERNSTEIN  (University  of  Halle).     The  Five  Senses  of  Man. 

Prof.  FERDINAND  COHN  (Breslau  University).  Thallophytes  (Alg^e,  Lichem 
Fungi). 

Prof.  HERMANN  (University  ol  Zurich).     Respiration. 

Prof.  LEUCKART  (University  of  Leipsic).     Outlines  of  A  nimal  Organization, 

Prof.  LIEBREICH  (University  of  Berlin).     Outlines  of  Toxicology. 

Prof.  KUNDT  (University  of  Strasburg).     On  Sound. 

Prof.  REES  (University  of  Eriangen).     On  Parasitic  Plants. 

Prof.  STEINTHAL  (University  of  Berlin).     Outlines  of  the  Science  of  Language. 

P.  BERT  (Professor  of  Physiology,  Paris).  Forms  of  Life  attd  other  Cosmical  Cur.* 
ditions,  •  — 

E.  ALGLAVE  (Professor  of  Constitutional  and  Administrative  Law  at  Douai,  and  ol 
Political  Economy  at  Lille).     The  Primitive  Elements  of  Political  Constitutions, 

P    LORAIN  (Professor  of  Medicine,  Paris).     Modern  Epidemics. 

Prof.  SCHUTZENBERGER  (Director  of  the  Chemical  Laboratory  at  the  Soff- 
bonne).     On  Fermentations. 

Mens.  FREIDEL.     The  Functions  of  Organic  Chemistry. 

Mons.  DEBRAY.     Precious  Metals. 

Prof.  CORFIELD,  M.  A-,  M.  D.  (Oxon.).     Air  in  its  Relation  to  Health, 

Prof.  A.  GIARD.     General  Embryology. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y, 


opinions  of  the  Press  on  the  *^  International  Scientific  Series.^ 


TyndalFs  Forms  of  Water. 

1  vol.,  l2mo.     Cloth.     Illustrated Price,  $1.50. 

"  In  the  volume  now  published,  Professor  Tyndall  has  presented  a  noble  illustration 
of  the  acuteness  and  subtlety  of  his  intellectual  powers,  the  scope  and  insight  of  his 
scientific  vision,  his  singular  command  of  the  appropriate  language  of  exposition,  and 
the  peculiar  vivacity  and  grace  with  which  he  unfolds  the  results  of  intricate  scientific 
research." — N.  Y.  Tribune. 

"  The  '  Forms  of  Water,'  by  Professor  Tyndall,  is  an  interesting  and  instructive 
little  volume,  admirably  printed  and  illustrated.  Prepared  expressly  for  this  series,  it 
is  in  some  measure  a  guarantee  of  the  excellence  of  the  volumes  that  will  follow,  and  an 
indication  that  the  publishers  will  spare  no  pains  to  include  in  the  series  the  freshest  in- 
vestigations of  the  best  scientific  minds." — 'Boston  yo7irnal. 

"  This  series  is  admirably  commenced  by  this  little  volume  from  the  pen  of  Prof. 
Tyndall.  A  perfect  master  of  his  subject,  he  presents  in  a  style  easy  and  attractive  his 
methods  of  investigation,  and  the  results  obtained,  and  gives  to  the  reader  a  clear  con- 
ception of  all  the  wondrous  transformations  to  which  water  is  subjected." — Churchman. 


II. 

Bagehot's  Physics  and  Politics. 

I  vol.,  l2nio.     Price,  $1.50. 

"  If  the  '  International  Scientific  Series  '  proceeds  as  it  has  begun,  it  will  more  than 
fialfil  the  promise  given  to  the  reading  public  in  its  prospectus.  The  first  volume,  by 
Professor  Tyndall,  was  a  model  of  lucid  and  attractive  scientific  exposition  ;  and  nox 
we  have  a  second,  by  Mr.  Walter  Bagehot,  which  is  not  only  very  lucid  and  charmingj^ 
but  also  original  and  suggestive  in  the  highest  degree.  Nowhere  since  the  publicatioii 
of  Sir  Henry  Maine's  'Ancient  Law,'  have  we  seen  so  many  fruitful  thoughts  sug- 
gested in  the  course  of  a  couple  of  hundred  pages.  .  .  .  To  do  justice  to  Mr.  Bage- 
hot's  fertile  book,  would  require  a  long  article.  With  the  best  of  intentions,  we  are 
conscious  of  having  given  but  a  sorry  account  of  it  in  these  brief  paragraphs.  But  we 
hope  we  have  said  enough  to  commend  it  to  the  attention  of  the  thoughtful  reader."—^ 
Prof.  John  Fiske,  in  the  A  tlantic  Monthly. 

"Mr.  Bagehot's  style  is  clear  and  vigorous.  We  refrain  from  giving  a  fuller  ac- 
count of  these  suggestive  essays,  only  because  we  are  sure  that  our  readers  will  find  it 
worth  their  while  to  peruse  the  book  for  themselves ;  and  we  sincerely  hope  that  the 
forthcoming  parts  of  the  'International  Scientific  Series'  will  be  as  Interesting."— 
A  thencetim. 

"  Mr.  Bagehot  discusses  an  Immense  variety  of  topics  connected  with  the  progress 
of  societies  and  nations,  and  the  development  of  their  distinctive  peculiarities;  and  hij 
book  shows  an  abundance  of  Ingenious  and  original  thought" — Alfred  Russeli 
Wallace,  in  Nature. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y, 


opinions  of  the  Press  on  the  ^^International  Scientific  Series,^ 


III. 


Foods^ 


By   Dr.  EDWARD    SMITH^ 
I  vol.,  i2mo.     Cloth.     Illustrated.      . Price,  $1.75. 

In  making  up  The  International  Scientific  Series,  Dr.  Edward  Smith  was  se- 
lected as  the  ablest  man  in  England  to  treat  the  important  subject  of  Foods.  His  services 
were  secured  for  the  undertaking,  and  the  little  treatise  he  has  produced  shows  that  the 
choice  of  a  writer  on  this  subject  was  most  fortunate,  as  the  book  is  unquestionably  the 
clearest  and  best-digested  compend  of  the  Science  of  Foods  that  has  appeared  in  our 
language. 

"  The  book  contains  a  series  of  diagrams,  dispfeying  the  effects  of  sleep  and  meals 
on  pulsation  and  respiration,  and  of  various  kinds  of  food  on  respiration,  which,  as  the 
results  of  Dr,  Smith's  own  experiments,  possess  a  very  high  value.  We  have  not  far 
to  go  in  this  work  for  occasions  of  favorable  criticism ;  they  occur  throughout,  but  are 
perhaps  rnost  apparent  in  those  parts  of  the  subject  with  which  Dr.  Smith's  name  is  es- 
pecially linked." — London  Examiiier. 

"The  union  of  scientific  and  popular  treatment  in  the  composition  of  this  work  will 
afford  an  attraction  to  many  readers  who_  would  have  been  indifferent  to  purely  theoreti- 
cal details.  .  .  .  Still  his  work  abounds  in  information,  much  of  which  is  of  great  value, 
apd  a  part  of  which  could  not  easily  be  obtained  from  other  sources.  Its  interest  is  de- 
cidedly  enhanced  for  students  who  demand  both  clearness  and  exactness  of  statement, 
by  the  profusion  of  well-executed  woodcuts,  diagrams,  and  tables,  which  accompany  the 
volume.  .  .  .  The  suggestions  of  the  author  on  the  use  of  tea  and  coffee,  and  of  the  va- 
rious  forms  of  alcohol,  although  perhaps  not  strictly  of  a  novel  character,  are  highly  in- 
structive, and  form  an  interesting  portion  of  the  volume."-— A^.  F.  Tribune. 


4 


IV. 

Body  and  Mind. 

THE    THEORIES    OF   THEIR    RELATION. 

By  ALEXANDER    BAIN,    LL.  D. 

I  vol.,   i2mo.      Cloth Price,   $1.50. 

Professor  Bain  is  the  author  of  two  well-known  standard  works  upon  the  Science 
»f  Mind — "The  Senses  and  the  Intellect,"  and  "The  Emotions  and  the  Will."  He  is 
one  of  the  highest  living  authorities  in  the  school  which  holds  that  there  can  be  no  sound 
or  valid  psychology  unless  the  mind  and  the  body  are  studied,  as  they  exist,  together. 

"  It_ contains  a  forcible  statement  of  the  connection  between  mind  and  body,  study- 
ing their  subtile  interworkings  by  the  light  of  the  most  recent  physiological  investiga- 
tions. The  summary  in  Chapter  V.,  of  the  investigations  of  Dr.  Lionel  Beale  of  the 
embodiment  of  the  intellectual  functions  in  the  cerebral  system,  will  be  found  the 
freshest  and  most  interesting  part  of  his  book.  Prof.  Bain's  own  theory  of  the  connec- 
tion between  the  mental  and  the  bodily  part  in  man  is  stated  by  himself  to  be  as  follows : 
There  is  '  one  substance,  with  two  sets  of  properties,  two  sides,  the  physical  and  tha 
mental — a  double-faced  ii7iity.'  While,  in  the  strongest  manner,  asserting  the  union 
of  mind  with  brain,  he  yet  denies  'the  association  of  union  /«  place,'  but  asserts  the 
union  of  close  succession  in  time,'  holding  that  'the  same  being  is,  by  alternate  fits,  un- 
der extended  and  under  un extended  consciousness."  ' — Christia7i  Register. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


Opijiions  of  the  Press  on  the  "  Interiiational  Scientific  Series.''^ 


The  Study  of  Sociology. 

By  HERBERT   SPENCER. 

I  vol.,  i2mo.     Cloth Price,  $1.50. 

"The  philosopher  whose  distinguished  name  gives  weight  and  influence  to  this  vol- 
ume, has  given  in  its  pages  some  of  the  finest  specimens  of  reasoning  in  all  its  forms 
and  departments.  There  is  a  fascination  in  his  array  of  facts,  incidents,  and  opinions, 
which  draws  on  the  reader  to  ascertain  his  conclusions.  The  coolness  and  calmness  of 
his  treatment  of  acknowledged  difficulties  and  grave  objections  to  his  theories  win  for 
him  a  close  attention  and  sustained  effort,  on  the  part  of  the  reader,  to  comprehend,  fol- 
low, grasp,  and  appropriate  his  principles.  This  book,  independently  of  its  bearing 
upon  sociology,  is  valuable  as  lucidly  showing  what  those  essential  characteristics  are 
which  entitle  any  arrangement  and  connection  of  facts  and  deductions  to  be  called  a 
science. ' ' — Episcopalian. 

"  This  work  compels  admiration  by  the  evidence  which  it  gives  of  immense  re- 
search, study,  and  observation,  and  is,  withal,  written  in  a  popular  and  very  pleasing 
style.     It  is  a  fascinating  work,  as  well  as  one  of  deep  practical  thought." — Bost.  Post. 

"  Herbert  Spencer  is  unquestionably  the  foremost  living  thinker  in  the  psychological 
and  sociological  fields,  and  this  volume  is  an  important  contribution  to  the  science  of 
which  it  treats.  ...  It  will  prove  more  popular  than  any  of  its  author's  other  creations, 
for  it  is  more  plainly  addressed  to  the  people  and  has  a  more  practical  and  less  specu- 
lative cast.  It  will  require  thought,  but  it  is  well  worth  tlunkiug  about." — Albany 
Evening  Jotirnal. 

VI. 

The   New  Chemistry. 

By  JOSIAH  P.  COOKE,  Jr., 

Erving  Professor  of  Chemistry  and  Mineralogy  in  Harvard  University. 
I  vol.,   i2mo.     Cloth Price,   $2.00. 

"  The  book  of  Prof  Cooke  is  a  model  of  the  modern  popular  science  work.  It  has 
just  the  due  proportion  of  fact,  philosophy,  and  true  romance,  to  make  it  a  fascinating 
companion,  either  for  the  voyage  or  the  study." — Daily  Graphic. 

"  This  admirable  monograph,  by  the  distinguished  Erving  Professor  of  Chemistry 
in  Harvard  University,  is  the  first  American  contribution  to  '  The  International  Scien- 
tific Series,'  and  a  more  attractive  piece  of  work  in  the  way  of  popular  exposition  upon 
a  difficult  subject  has  not  appeared  in  a  long  time.  It  not  only  well  sustains  the  char- 
acter of  the  volumes  with  which  it  is  associated,  but  its  reproduction  in  European  coun- 
tries will  be  an  honor  to  American  science." — Neiv  York  Tribune, 

"  All  the  chemists  in  the  country  will  enjoy  its  perusal,  and  many  will  seize  upon  it 
as  a  thing  longed  for.  For,  to  those  advanced  students  who  have  kept  well  abreast  oi 
the  chemical  tide,  it  offers  a  calm  philosophy.  To  those  others,  youngest  of  the  class, 
who  have  emerged  from  the  schools  since  new  methods  have  prevailed,  it  presents  a 
generalization,  drawing  to  its  use  all  the  data,  the  relations  of  which  the  newly-fledged 
fact-seeker  may  but  dimly  perceive  without  its  aid.  .  .  .  To  the  old  chemists.  Prof 
Cooke's  treatise  is  like  a  message  from  beyond  the  mountain.  They  have  heard  0/ 
changes  in  the  science ;  the  clash  of  the  battle  of  old  and  new  theories  has  stirred  them 
from  afar.  The  tidings,  too,  had  come  that  the  old  had  given  way ;  and  little  more  than 
this  they  knew.  .  .  .  Prof  Cooke's 'New  Chemistry' must  do  wide  service  in  bringing 
to  close  sight  the  little  known  and  the  longed  for.  ...  As  a  philosophy  it  is  elemen' 
tary,  but,  a^  a  book  of  science,  ordinary  readers  will  find  it  sufficiently  advanced."-' 
Utica  Mor7ting  Herald. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


Opiniotis  of  the  Press  oti  the  '■'' Internatioftal  Scientific  Series." 


VII. 

The  Conservation  of  Energy. 

By  BALFOUR  STEWART,  LL.  D.,  F.  R.  S. 

With  an  Appendix  treatmg  of  the  Vital  and  Mejiial  Applications  of  the  Doctri7ie. 

I  vol.,  i2mo.     Cloth.     Price,  $1.50. 

"  The  author  has  succeeded  In  presenting  the  facts  in  a  clear  and  satisfactory  manner, 
using  simple  language  and  copious  illustration  in  the  presentation  of  facts  and  prin- 
ciples, confining  himself,  however,  to  the  physical  aspect  of  the  subject.  In  the  Ap- 
pendix the  operation  of  the  principles  in  the  spheres  of  Hfe  and  mind  is  supplied  by 
the  essays  of  Professors  Le  Conte  and  Bain." — Ohio  Partner. 

"  Prof.  Stewart  is  one  of  the  best  known  teachers  in  Owens  College  in  Manchester. 

"The  volume  of  The  International  Scientific  Series  now  before  us  is  an  ex- 
cellent  illustration  of  the  true  method  of  teaching,  and  will  well  compare  with  Prof. 
Tyndall's  charming  little  book  in  the  same  series  on  *  Forms  of  Water,"  with  illustra- 
tions enough  to  make  clear,  but  not  to  conceal  his  thoughts,  in  a  style  simple  and 
brief." — Christian  Register,  Boston. 

"  The  writer  has  wonderful  ability  to  compress  much  information  into  a  few  words. 
It  is  a  rich  treat  to  read  such  a  book  as  this,  when  there  is  so  much  beauty  and  force 
combined  with  such  simplicity. — Eastern  Press. 


VJII. 

Animal  Locomotion; 

Or,  WALKING,   S\VIMMING,  AND  FLYING. 

With  a  Dissertation  on  Aeronautics. 

By  J.  BELL  PETTIGREW,  M.  D.,  F.  R.  S.,  F.  R.  S.  E., 
F.  R.C.  P.E. 

I  vol.,  i2mo Price,  $1,75.^ 

"  This  work  is  more  than  a  contribution  to  the  stock  of  entertaining  knowledge, 
though,  if  it  only  pleased,  that  would  be  sufficient  excuse  for  its  publication.  But  Dr. 
Pettigrew  has  given  his  time  to  these  investigations  with  the  ultimate  purpose  of  solv- 
ing the  difficult  problem  of  Aeronautics.  To  this  he  devotes  the  last  fifty  pages  of  hi« 
book.  Dr.  Pettigrew  is  confident  that  man  will  yet  conquer  the  domain  of  the  air."—' 
N.   Y.  Jotirnal  of  Commerce. 

"  Most  persons  claim  to  know  how  to  walk,  but  few  could  explain  the  mechanictij 
principles  involved  in  this  most  ordinary  transaction,  and  will  be  surprised  that  the 
movements  of  bipeds  and  quadrupeds,  the  darting  and  rushing  motion  of  fish,  and  the 
erratic  flight  of  the  denizens  of  the  air,  are  not  only  anologous,  but  can  be  reduced  to 
similar  formula.  The  work  is  profusely  illustrated,  and,  without  reference  to  the  theory 
it  is  designed  to  expound,  will  be  regarded  as  a  valuable  addition  to  natural  history.'' 
'—Omaha  Republic. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y, 


opinions  of  the  Press  on  the  ^^International  Scientific  Series" 


IX. 

Responsibility  in  Mental  Disease. 

By  HENRY   MAUDSLEY,    M.  D., 

Fello.y  of  the  Royal  College  of  Physicians;  Professor  of  Medical  Jurisprudence 
in  University  College,  London. 

I  vol.,   i2mo.     Cloth.     .   •.     Price,  $1.50. 

"  Having  lectured  in  a  medical  college  on  Mental  Disease,  this  book  has  been  a 
feast  to  us.  It  handles  a  great  subject  in  a  masterly  manner,  and,  in  our  judgment,  the 
positions  taken  by  the  author  are  correct  and  well  sustained." — Pastor  aftd  People. 

"  The  author  is  at  home  in  his  subject,  and  presents  his  views  in  an  almost  singu- 
larly clear  and  satisfactory  manner.  .  .  .  The  volume  is  a  valuable  contribution  to  one 
of  the  most  difficult,  and  at  the  same  time  one  of  the  most  important  subjects  of  inves- 
tigation at  the  present  day." — N.  Y.  Observer. 

"  It  is  a  work  profound  and  searching,  and  abounds  in  wisdom." — Pittsburg  Co7n~ 
inercial. 

"  Handles  the  important  topic  with  masterly  power,  and  its  suggestions  are  prac- 
tical and  of  great  value." — Providence  Press. 

X. 

The  Science  of  Law. 

By  SHELDON  AMOS,  M.  A., 

Professor  of  Jurisprudence  in  University  College,  London;  author  of  "A  Systematic 

View  of  the  Science  of  Jurisprudence,"  "  An  English  Code,  its  Difficulties 

and  the  Modes  of  overcoming  them,"  etc.,  etc. 

I  vol.,   i2mo.     Cloth Price,  $1.75. 

"The  valuable  series  of  'International  Scientific*  works,  prepared  by  eminent  spe- 
cialists, with  the  intention  of  popularizing  information  in  their  several  branches  of 
knowledge,  has  received  a  good  accession  in  this  compact  and  thoughtful  volume.  It 
is  a  difficult  task  to  give  the  outlines  of  a  complete  theory  of  law  in  a  portable  volume, 
which  he  who  runs  may  read,  and  probably  Professor  Amos  himself  would  be  the  last 
to  claim  that  he  has  perfectly  succeeded  in  doing  this.  But  he  has  certainly  done  much 
to  clear  the  science  of  law  from  the  technical  obscurities  which  darken  it  to  minds  which 
have  had  no  legal  training,  and  to  make  clear  to  his  '  lay '  readers  in  how  true  and  high  a 
sense  it  can  assert  its  right  to  be  considered  a  science,  and  not  a  mere  practice." — Thi 
Christian  Register. 

"The  works  of  Bentham  and  Austin  are  abstruse  and  philosophical,  and  Maine's 
require  hard  study  anda  certain  amount  of  special  training.  The  writers  also  pursue 
different  lines  of  investigation,  and  can  only  be  regarded  as  comprehensive  in  the  de- 
partments they  confined  themselves  to.  It  was  left  to  Amos  to  gather  up  the  result 
and  present  the  science  in  its  fullness.  The  unquestionable  merits  of  this,  his  last  book, 
are,  that  It  contains^  a  complete  treatment  of  a  subject  which  has  hitherto  been  handled 
by  specialists,  and  it  opens  up  that  subject  to  every  inquiring  mind.  ...  To  do  justice 
to  '  The  Science  of  Law'  ^yould  require  a  longer  review  than  we  have  space  for.  We 
have  read  no  more  interesting  and  instructive  book  for  some  time.  Its  themes  concern 
every  one  who  renders  obedience  to  laws,  and  who  would  have  those  laws  the  best 
possible.  The  tide  oHegal  reform  which  set  in  fifty  years  ago  has  to  sweep  yethighei 
If  the  flaws  In  our  jurisprudence  are  to  be  removed.  The  process  of  change  cannot  be 
better  guided  than  by  a  well-informed  public  mind,  and  Prof.  Amos  has  done  great 
service  in  materially  helping  to  promote  this  end." — -Buffalo  Courier. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadv/ay,  N.  Y. 


opinions  of  the  Press  on  the  ^'■International  Scientific  Series.'^ 


XI. 

Animal  Mechanism, 

A  Treatise  on  Terrestrial  and  Aerial  Locojnotion. 

By  E.  J.  MAREY, 

Professor  at  the  College  of  France,  and   Member  of  the  Academy  of  Medicine, 

With  117  Illustrations,  drawn  and  engraved  under  the  direction  of  the  author- 

I  vol.,  i2mo.     Cloth Price,  $1.75 

"  We  hope  that,  in  the  short  glance  which  we  have  taken  of  some  of  the  most  im- 
portant points  discussed  in  the  work  before  us,  we  have  succeeded  in  interesting  our 
readers  sufficiently  in  its  contents  to  make  them  curious  to  learn  more  of  its  subject- 
matter.     We  cordially  recommend  it  to  their  attention. 

"The  author  of  the  present  work,  it  is  well  known,  stands  at  the  head  of  those 
physiologists  who  have  investigated  the  mechanism  of  animal  dynamics — indeed,  we 
may  almost  say  that  he  has  made  the  subject  his  own.  By  the  originality  of  his  con- 
ceptions, the  ingenuity  of  his  constructions,  the  skill  of  his  analysis,  and  the  persever- 
ance of  his  investigations,  he  has  surpassed  all  others  in  the  power  of  unveiling  the 
complex  and  intricate  movements  of  animated  beings." — Popular  Science  Monthly. 


XII. 

History   of  the    Conflict    between 
Religion  and   Science. 

By  JOHN  WILLIAM  DRAPER,  M.  D.,  LL.  D., 

Author  of  "  The  Intellectual  Development  of  Europe." 
I  vol.,  i2mo. Price,  $1.75. 

"This  little  '  History'  would  have  been  a  valuable  contribution  to  literature  at  any 
^ime,  and  is,  in  fact,  an  admirable  text-book  upon  a  subject  that  is  at  present  engross- 
ing the  attention  of  a  large  number  of  the  most  serious-minded  people,  and  it  is  no 
small  compliment  to  the  sagacity  of  its  distinguished  author  that  he  has  so  well  gauged 
the  requirements  of  the  times,  and  so  adequately  met  them  by  the  preparation  of  this 
volume.  It  remains  to  be  added  that,  while  the  writer  has  flinched  from  no  responsi- 
bility in  his  statements,  and  has  written  with  entire  fidelity  to  the  demands  of  truth 
and  justice,  there  is  not  a  word  in  his  book  that  can  give  offense  to  candid  and  fair- 
minded  readers." — A''.  Y.  Evening  Post. 

"  The  key-note  to  this  volume  is  found  in  the  antagonism  between  the  progressive 
tendencies  of  the  human  mind  and  the  pretensions  of  ecclesiastical  authority,  as  devel- 
oped in  the  history  of  modern  science.  No  previous  writer  has  treated  the  subject 
from  this  point  of  view,  and  the  present  monograph  will  be  found  to  possess  no  less 
originality  of  conception  than  vigor  of  reasoning  and  wealth  of  erudition.  .  .  .  The 
method  of  Dr.  Draper,  in  his  treatment  of  the  various  questions  that  come  up  for  dis- 
cussion, is  marked  by  singular  impartiality  as  well  as  consummate  ability.  Through- 
out his  work  he  maintains  the  position  of  an  historian,  not  of  an  advocate.  His  tone  is 
tranquil  and  serene,  as  becomes  the  search  after  truth,  with  no  trace  of  the  impassioned 
ardor  of  controversy.  He  endeavors  so  far  to  identify  himself  with  the  contending 
parties  as  to  gain  a  clear  comprehension  of  their  motives,  but,  at  the  same  time,  he 
submits  their  actions  to  the  tests  of  a  cool  and  impartial  examination." — N.  Y.  Tribune. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


opinions  of  the  Press  on  the  "  International  Scientific  Series P 

XIII. 

THE    DOCTRINE   OF 

escent,    and    Darwinism. 

By  OSCAR  SCHMIDT, 
PFofessor  in  the  University  of  Strasburg. 

With  26  Woodcuts. 
I  vol.,  121110.     Cloth Price,   $1.50. 

"The  entire  subject  is  discussed  with  a  freshness,  as  well  as  an  elaboration  of  de- 
tail, that  renders  his  work  interesting  in  a  more  than  usual  degree.  The  facts  upon 
which  the  Darwinian  theory'  is  based  are  presented  in  an  effective  manner,  conclusions 
are  ably  defended,  and  the  question  is  treated  in  more  compact  and  available  style 
than  in  any  other  work  on  the  same  topic  that  has  yet  appeared.  It  is  a  valuable  ad- 
dition to  the  '  International  Scientific  Series.'  " — Boston  Post. 

"  The  present  volume  is  the  thirteenth  of  the  'International  Scientific  Series,'  and 
is  one  of  the  most  interesting  of  all  of  them.  The  subject-matter  is  handled  with  a 
great  deal  of  skill  and  earnestness,  and  the  courage  of  the  author  in  avowing  his  opin- 
ions is  much  to  his  credit.  .  .  .  This  volume  certainly  merits  a  careful  perusal." — 
Hartford  Evening  Post. 

"  The  volume  which  Prof.  Schmidt  has  devoted  to  this  theme  is  a  valuable  contri- 
bution to  the  Darwinian  literature.  Philosophical  in  method,  and  eminently  candid, 
it  shows  not  only  the  ground  which  Darwin  had  In  his  researches  made,  and  conclu- 
"sions  reached  before  him  to  plant  his  theory  upon,  but  shows,  also,  what  that  theory 
really  Is,  a  point  upon  which  many  good  people  who  talk  very  earnestly  about  the 
matter  are  very  Imperfectly  informed." — Detroit  Free  Press. 


XIV. 

The  Chemistry  of  Light  and 
Photography ; 

In   its  Application  to  Art,  Science,  and   Industry. 

By  Dr.  HERMANN  VOGEI, 
Professor  In  the  Royal  Industrial  Academy  of  Berlin. 

With  100  Illustrations. 
i2mo Price,  $2.00. 

_"  Out  of  Photography  has  sprung  a  new  science — the  Chemistry  of  Light — and,  in 
giving  apopular  view  to  the  one,  Dr.  Vogel  has  presented  an  analysis  of  the  principles 
and  processes  of  the  other.  His  treatise  is  as  entertaining  as  it  is  instructive,  pleas- 
antly combining  a  history  of  the  progress  and  practice  of  photography — from  the  first 
rough  experiments  of  Wedgwood  and  Davy  with  sensitized  paper,  in  1802,  down  to 
the  latest  improvements  of  the  art — with  technical  illustrations  of  the  scientific  theories 
on  which  the  art  is  based.  It  is  the  first  attempt  in  any  manual  of  photography  to  set 
forth  adequately  the  just  claims  of  the  Invention,  both  from  an  artistic  and  a  scientific 
point  of  view,  and  it  must  be  conceded  that  the  effort  has  been  ably  conducted."—' 
Chicago  Tribune. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


opinions  of  the  Press  on  the  ^^International  Scientific  Series."*^ 


XV. 

Fungi ; 

THEIR   NATURE,  INFLUENCE,  AND    USES. 

By  M.  C.   COOKE,  M.  A.,  LL.  Z>. 

Edited  by  Rev.  M.  J.  BERKELEY,  M.  A.,  F.  L.  S. 

With  109  Illustrations.     Price,  $1.50. 

"Even  if  the  name  of  the  author  of  this  work  were  not  deservedly  eminent,  that  of 
the  editor,  who  has  long  stood  at  the  head  of  the  British  fungologists,  would  be  a  suf- 
ficient voucher  for  the  accuracy  of  one  of  the  best  botanical  monographs  ever  issued 
from  the  press.  .  .  .  The  structure,  germination,  and  growth  of  all  these  widely-dif- 
fused organisms,  their  habitats  and  influences  for  good  and  evil,  are  systematically 
described." — New  York  World. 

"Dr.  Cooke's  book  contains  an  admirable  rhtinid oi  what  is  known  on  the  struct- 
ure, growth,  and  reproduction  of  fungi,  together  with  ample  bibliographical  references . 
to  original  sources  of  information." — Lo?idoji  Athejicewn. 

"The  production  of  a  work  like  the  one  now  under  review  represents  a  large 
amount  of  laborious,  difficult,  and  critical  work,  and  one  in  which  a  serious  slip  or  fatal 
error  would  be  one  of  the  easiest  matters  possible,  but,  as  far  as  we  are  able  to  judge, 
the  new  hand-book  seems  in  every  way  well  suited  to  the  requirements  of  all  beginners 
in  the  difficult  and  involved  study  of  fungology." — The  Gardetier's  Chronicle  {Lon- 
don). 

XVI. 

The  Life  and  Growth  of  Language: 

AN    OUTLINE     OF    LINGUISTIC    SCIENCE. 
By  WILLIAM  DWIGHT  WHITNEY, 

Professor  of  Sanskrit  and  Comparative  Philology  in  Yale  College. 
I  vol.,  i2mo.     Cloth.     Price,  $1.50. 

"  Prof  Whitney  is  to  be  commended  for  giving  to  the  public  the  results  of  his  ripe 
scholarship  and  unusually  profound  researches  in  simple  language.  He  draws  illus- 
trations and  examples  of  the  principles  which  he  wishes  to  impact,  from  common  life 
and  the  words  in  frequent  use. 

"  The  topics  discussed  in  this  volume  are,  for  the  most  part,  those  which  have 
been  already  treated  by  other  writers  on  philology,  and  even  by  the  author  himself,  in 
his  volume  on  '  Language,  and  the  Study  of  Language,'  published  a  few  years  ago, 
and,  though  many  of  the  truths  here  set  forth  are  those  with  which  students  in  the 
same  line  of  investigation  are  generally  familiar,  all  will  rejoice  to  see  them  restated  in 
such  a  fresh  and  simple  way. 

"This  work,  while  valuable  to  scholars,  will  be  interesting  to  every  one." — The 
Chu7xhma7i.  * 

"  This  work  is  an  important  contribution  to  a  science  which  has  advanced  steadily 
under  conditions  that  appear  constantly  to  throw  an  increasing  light  on  difficult  ques- 
tions, and  at  each  step  clear  the  way  for  further  discoveries." — Chicago  Inter-Occan. 

"  Prof.  Whitney  is  undoubtedly  one  of  the  foremost  of  English-speaking  philologists, 
and  occupies  an  enviable  position  in  the  wider  circle  of  European  students  of  language. 

"His  style,  clear,  simple,  picturesque,  abounding  in  striking  illustrations,  and  apt 
in  comparisons,  is  admirably  fitted  to  be  the  vehicle  of  a  popular  treatise  like  the  work 
under  consideration." — Po7-tla7id  Daily  Press. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


opinions  of  the  Bress  on  the  ''^  International  Scientific  Series y 

XVII. 

Money  and  the  Mechanism  of  Ex- 
change. 

By  W.  STANLEY  JEVONS,  M.  A.,  F,  R.  S., 

Professor  of  Logic  and  Political  Economy  in  the  Owens  College,  Manchester. 

I  vol.,  i2mo.     Cloth.     Price,  $1.75. 

"  He  offers  us  what  a  clear-sighted,  cool-headed,  scientific  student  has  to  say  on  the 
nature,  properties,  and  natural  laws  of  money,  without  regard  to  local  interests  or  na- 
tional bias.  His  work  is  popularly  written,  and  every  page  is  replete  with  solid  instruc- 
tion of  a  kind  that  Is  just  now  lamentably  needed  by  multitudes  of  our  people  who  are 
victimized  by  the  grossest  fallacies." — Popular  Science  Monthly. 

"  If  Professor  J evons's  book  is  read  as  extensively  as  it  deserves  to  be,  we  shall 
have  sounder  views  on  the  use  and  abuse  of  money,  and  more  correct  ideas  on  what  a 
circulating  medium  really  means." — Boston  Saturday  Eventing  Gazette. 

"Professor  Jevons  writes  m  a  sprightly  but  colorless  style,  without  trace  of  either 
prejudice  or  mannerism,  and  shows  no  commitment  to  any  theory.  The  time  is  not 
very  far  distant,  we  hope,  -when  legislators  will  cease  attempting  to  legislate  upon 
money  before  they  know  what  money  is,  and,  as  a  possible  help  toward  such  a  change. 
Professor  Jevons  deserves  the  credit  of  having  made  a  useful  contribution  to  a  depart- 
ment of  study  long  too  much  neglected,  but  of  late  years,  we  are  gratified  to  say,  be- 
coming less  so." — The  Financier,  New  York. 


XVIII. 

The  Nature  of  Light, 

WITH   A  GENERAL  ACCOUNT  OF   PHYSICAL  OPTICS. 
By  Dr.  EUGENE  LOMMEL 

(University  of  Erlangen). 
I  vol.,  i2mo.     Cloth.         .         .         .         Price,  $2.00. 

*'  In  the  present  treatise.  Professor  Lommel  has  given  an  admirable  outline  of  the 
nature  of  light  and  the  laws  of  optics. 

"  Unlike  most  other  writers  on  this  subject,  the  author  has,  we  think,  wisely  post- 
poned all  reference  to  theories  of  the  nature  of  light,  until  the  laws  of  reflection,  re- 
fraction, and  absorption,  have  been  clearly  set  before  the  reader.  Then,  in  the  fifteenth 
chapter,  Professor  Lommel  discusses  Fresnel's  famous  interference  experiment,  and 
leads  the  reader  to  see  that  the  undulatory  theory  is  the  only  conclusion  that  can  be 
satisfactorily  arrived  at.  A  clear  exposition  is  now  given  of  Huyglien's  theory,  after 
which  follow  several  chapters  on  the  diffraction  and  polarization  of  light-bearing  waves. 

"  The  reader  is  thus  led  onward  much  in  the  same  way  as  the  science  itself  has  un- 
folded, and  this,  we  think,  is  the  surest  and  best  way  of  teaching  natural  knowledge. 

"We  have  said  enough  to  show  that  Professor  Lommel's  treatise  is  a  useful  contri- 
bution to  the  '  International  Series ' — a  book  that  can  thoroughly  be  understood  and 
enjoyed  by  any  intelligent  reader  who  may  not  have  had  any  special  scientific  tram- 
ing. ' ' — Nattire. 

"  In  a  style  singularly  lucid,  considering  the  abstruse  nature  of  the  subject  treated. 
Dr.  Lommel  unfolds  the  learning  of  the  scientists  on  the  nature  and  phenomena  of 
light." — Philadelphia  Inquirer. 

"  As  a  popular  introduction  to  physical  optics,  it  would  be  difficult  to  find  a  more 
satisfactory  work  than  the  one  by  Dr.  Lommel,  which  has  just  appeared  in  the  excel- 
lent '  International  Scientific  Series.'  " — The  Eiiglish  Mechanic. 

D,  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y, 


A  New  Magazine  for  Students  and  Cultkated  Readers. 


THE 


POPULAR  SCIENCE  MONTHLY, 

CONDUCTED    BY 
Profeseor  E.    L.   VOUMANS. 

The  growing  importance  of  scientific  knowledge  to  all  classes  of  the 
community  calls  for  more  efficient  means  of  diffusing  it.  The  Popular 
Science  Monthly  has  been  started  to  promote  this  object,  and  supplies  a 
want  met  by  no  other  periodical  in  the  United  States. 

It  contains  instructive  and  attractive  articlesj  and  abstract?  of  articles, 
original,  selected,  and  illustrated,  from  the  leading  scientific  men  of  differ- 
ent countries,  giving  the  latest  interpretations  of  natural  phenomena,  ex- 
plaining the  applications  of  science  to  the  practical  arts,  and  to  the  opera- 
tions of  domestic  life. 

It  is  designed  to  give  especial  prominence  to  those  branches  of  science 
which  help  to  a  better  understanding  of  the  nature  of  man ;  to  present  the 
claims  of  scientific  education  ;  and  the  bearings  of  science  upon  questions 
of  society  and  government.  How  the  various  subjects  of  current  opinion 
are  affected  by  the  advance  of  scientific  inquiry  will  also  be  considered. 

In  its  literary  character,  this  periodical  aims  to  be  popular,  without  be- 
ing superficial,  and  appeals  to  the  intelligent  reading-classes  of  the  commu- 
nity. It  seeks  to  procure  authentic  statements  from  men  who  know  their 
subjects,  and  who  will  address  the  non-scientific  public  for  purposes  of  ex- 
position and  explanation. 

It  will  have  contributions  from  Herbert  Spencer,  Professor  Huxley, 
Professor  Tyndall,  Mr.  Darwin,  and  other  writers  identified  with  specu- 
lative thought  and  scientific  investigation. 

THE  POPULAR  SCIENCE  MONTHLY  is  published  in  a  large 
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or  Fifty  Cents  per  copy, 

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country." — Hoine  Journal. 

"  The  initial  number  is  admirably  constituted." — Evening-  Mail. 

"  In  our  opinion,  the  right  idea  has  been  happily  hit  in  the  plan  of  this  new  monthly." 
'—Bttffalo  Cotirier. 

"  A  journal  which  promises  to  be  of  eminent  value  to  the  cause  of  popular  education  in 
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IMPORTANT  TO  CLUBS. 

The  Popular  Science  Monthly  will  be  supplied  at  reduced  rates  with  any  periodi- 
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Any  person  remitting  Twenty  Dollars  for  four  yearly  subscriptions  will  receive  an  e.x- 
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The  Popular  Science  Monthly  and  Appletons'  Journal  (weekly),  per  annum,  $8.oc 

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Remittances  should  be  made  by  postal  money-order  Dr  check  to  the  Publishers, 

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Boston  College  Library 

Chestnut  Hill,  Mass.    02167 


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